For one, BDSM is done between consenting adults. A sort of guideline for BDSM can be summed up in the phrase 'Safe. Sane. Consensual'. Abuse is all about power and control. While yes, those elements exist in BDSM play, they are not its end goals. Ultimately, the purpose of BDSM is to explore kinks with your partner, and to build trust.
In BDSM play, you have two roles: the Dominant, and the submissive (Their are other names, but this is the basic). Together, they perform a scene (a scenario of sorts), the submissive is typically a masochist, and the Dominant, a sadist. Essentially, the submissive receives pleasure from being spanked, tied up, ordered around, etc -- and the Dominant receives pleasure from doing those and fulfilling the submissive's kinks. It is the responsibility of the Dominant to not only perform these things, but to also ensure their submissive isn't put into any real danger.
Bondage without adequate knowledge can be quite dangerous, it can cause nerve damage, loss of circulation, blood clots, and even death in severe cases. So the Dominant must also be on the watch and learn how to read a submissive's body language. Are they wiggling their fingers? Are they rotating their ankles? etc. These are signs that the ropes (or other medium) are too tight, and are cutting off feeling or circulation.
So where does trust and the power dynamic play into this? It's seen that Dominants in a BDSM D/s relationship have all the power, while this is somewhat true, this power is given voluntarily by the submissive. In a scene, the submissive can stop the scene at any time, there are no ifs, ands, or buts. The Dominant will untie, or do whatever else needed to release the submissive, and the scene will end. This is governed by, what I view should be the most important thing in BDSM play, the safeword. You see, throughout a scene, and within a BDSM relationship, communication is paramount, and there is always communication going on between a Dominant and the submissive, even if it's non-vocal.
Before a scene begins, a safeword will be established, this indicates that, should it be spoken, the scene will end, no exceptions. In cases where vocal communication isn't possible, such as a gag being used, there are other methods such as the submissive holding a set of heavy coins (or other object capable of making a distinct, clear noise) in their hands. If the submissive drops this, the scene ends, no exceptions. This is also where the Dominant's observation, and communication becomes very important.
Because bondage can cause injury, it's imperative that the Dominant watch body language, and assess the submissive constantly during play. Because there is a time within a scene where communication with a submissive stops being possible. This is known as subspace.
Subspace is the moment in a scene, where the submissive undergoes a spike of adrenaline and endorphins that can cause them to enter varying levels of altered psychological states from a feeling of being high, to a trance-like state where communication can be difficult to establish between a submissive and a Dominant. When a submissive enters subspace, the Dominant must quickly end the scene and release them. At which point, they will monitor the submissive carefully and administer Aftercare.
Aftercare is immensely important for a submissive's well-being. Once subspace subsides, a sub will enter what is called a subdrop, this is an endorphin crash where they will feel weakened, fatigued, and may have difficulty concentrating. A Dominant will care for the submissive, have them drink water, and eat, and provide close contact such as cuddling. They will also discuss the scene, what they liked, what they disliked, if they should try something again or how to do something differently. Without aftercare, a submissive can develop flue-like symptoms, and become depressed. Aftercare solidifies the emotional bond between a Dominant and submissive, and strengthens the trust within the relationship.
And that's all BDSM is, it's a relationship built on a very strong emotional bond, and immense trust between two consenting adults. Because of the stakes within such a dynamic, not communicating isn't an option, doing so can lead to injury or worse. Knowing this as a submissive and a Dominant is extremely important for both of their safety and well-being. I like to argue that BDSM relationships are much more open than regular relationships thanks to this policy, because it's dependent on being very open with your partner to ensure that your emotional and physical needs are met.
Community-wise, the BDSM community is also very open, and most are more than willing to help people interested. There are BDSM clubs, munches (a lunch where practitioners meet up), and conventions. There's tons, and I mean TONS of information online, including several official wikis and forums loaded with information that is helpful and people willing to help out those interested.
That said, having explained these things, there are people within the community to watch out for, because there is always that one. And I feel it irresponsible of me not to give out a fair warning.
Generally, avoid people that call themselves Master/Mistress. These titles are earned, and anyone bragging about their title needs to be avoided greatly. The reason is, at least in typical BDSM culture, is that Master/Mistress is a title given to someone who is very, very experienced and well knowledgeable in BDSM by others in the community.
Secondly, avoid people who say they don't do Aftercare, or that it's not important. Or that they don't do safewords. This is a massive red flag for someone who isn't interested in your safety, nor health, and can be a quick road to injury or a really, really bad situation.
Thirdly, avoid coercion. BDSM is about openness and exploring kinks together. You do not have to do anything, and should not do anything outside of your comfort zone.
These types of people are watched out for in the community, and other members will have no issue informing you of who to avoid.
The only other thing left I can think of to talk about is collars. Collars have a special significance in BDSM culture, and it's important to know how they work and what they mean. A collar is a device that the submissive wears around the neck, they come in many varieties, and many styles, and have many functions. There are also two types of collars: a typical collar, and a play-collar. In the typical culture of BDSM, a collar signifies the absolute trust and strength of a bond shared between a Dominant and their submissive.
Do note, that being collared is a voluntary process where the submissive is giving up their power to their Dominant. This is extensively discussed beforehand to determine if that's where both the D/s want their relationship to go, and must be mutually agreed upon. Do not let anyone try and convince you otherwise.
As such, it's significance has a similar weight to an engagement ring for many couples, or a statement that this submissive is 'owned' (collared) and in a relationship with their Dominant. When a submissive wears a collar, it is usually given to them by their Dominant, and only the Dominant is allowed to remove the collar (barring cases such as medical emergencies).
It's important to know that you shouldn't touch or mess with the collar of a submissive who belongs to another Dominant. Collaring a submissive may have certain rituals and traditions associated with it, and generally a Dominant may lay down a series of rules for a submissive who has been collared (breaking of these rules results in punishment for the submissive as an example, and a submissive may willingly try and break the rules to get punished).
The other type of collar is a play-collar. These are also worn around the neck, but are temporary and used in a particular scene. Often, they are fastened to a rope or chain, a lead, and allow the Dominant to lead their submissive around. Once the scene has finished, they are removed.
Finally, as I pointed out in another post. Ask, ask, ask. I cannot stress this enough. If you don't know something, ask. It's really for your well-being, and we'd all rather you have fun, and do so in a healthy, and safe manner. This is especially important for Dominants. Because you will be responsible for the well-being of a submissive, and are also exploring things yourself, it's important you ask and try to learn as much as you can.
My rule of thumb is: If you're not sure, don't do it. There's also nothing wrong with a Dominant playing a submissive to learn. Trust me, no one's going to think anything less of you, the community isn't one to judge.
So, remember. Safe. Sane. Consensual. This is what separates BDSM from abuse. The former is all about the bond, the trust, and the exploration. The latter cares nothing for that.