Warlocks are not a good introduction to the magic system in D&D because they work so differently from every other caster, however, they are quite interesting indeed and were also my first spellcaster and so far my favorite class even though I'm a better Rogue or Bard and am enjoying playing a Paladin.
First of all do remember that you have the best cantrip in the entire game, Eldritch Blast FORCE damage, scales with level and is upgradable through invocations to do even more damage, have more range and even push back enemies, happens to combo really well with the Warlock exclusive spell Hex, in any case, due to your limited amount of spells this will be your bread and butter, yes even if you play a Pact of the Blade you will eventually stop using you pact weapon, so I'd advise against that and would recommend Pact of the Tome, you are probably going to get a lot more use out of your spells if you are able to cast them as rituals[footnote]While they still consume ingredients, instead of consuming a slot spells when cast as rituals take time, listed individually on each spell is whether or not they can be cast as rituals and how long they take to be cast as rituals, definitely a good solid option.[/footnote].
In any case, one of your strengths is that since you always use your highest slot available to cast your spell you can get a lot of use out of scaleable spells like Magic Missile, since ou are always going to be casting it at your highest available slot, also due keep in mind that since the Mystic Arcanum spells[footnote]The only way you can cast spells of 6th, 7th, 8th and 9th Level.[/footnote] are technically a spell-like ability granted to you by your patron instead of an actual spell you don't really need materials to cast them, which makes up a little bit for the fact that you only get one of each level, because at least you can cast them consistently every long rest without worrying for the materials.
In any case, Warlocks are interesting characters to play but only if you are more into the role-playing aspect of the game, they can do a little bit of most things but their use in combat is going to be very limited outside of mostly spamming Eldritch Blast, which is strong but you aren't going to be doing cool magic all over the place like a Wizard, Sorcerer, Cleric or even a Bard, hell even the Paladin and the Ranger have more spell uses per day than you do and they can actually fight, but it's your Invocations where you get your strength from and though there are some good things for combat in there if you actually read through them, well they allow you to do actually a lot of cool role-playing things, like reading all languages, being able to detect Magic at will for free, being able to use disguise self at will and so on, shit that combos really well with Charisma as your main stat, because as a Warlock you can be a really good scheming kind of character, I love it because I mostly don't care about combat, RP is the reason I play these games and Warlock is very good at that, not really my most used class but I always look forward to playing one, best of luck with your Warlock but if you really want to be a Spellcaster I would suggest you switch classes because even the Ranger is more of a Spellcaster, Warlocks are all about flavour and not much else besides that.
