Ok so to your first question, a games designer is a broad term in itself, as a designer will have many different and maybe specific jobs. For example you may have a Designer working on all the maps, or a designer who decides what gameplay elements are in the game. They will usually get input from the rest of the studio but it is up to them what is in the final game.
Designing a game is only one side of a video game, as you will have Programmers, Artists, Producers, QA(Quality Assurance). But the main ones are Programmers and Artists, both of which have many many sub-categories.
Programmers
These are the guys/girls that make the game work, if you press a button on your controller the game knows what to do with that input via a programmer. Thats the most obvious role a programmer may have, but you will have tonnes of the people working on background elements such as :
- Graphics, Rendering, Lighting, Animation Engine
-- This branch is all to do with the Graphics of game, there are a lot of rendering techniques out there with more being used as our technology becomes more efficient.
- AI
-- This branch is all to do with how the computer handles situations when you play, for example when you play an RTS game, the enemy computer will decide what to do based off the environment it is in.
- UI (User Interface) or HUDs (Heads-Up-Display)
-- This branch is usually quite small. Here the programmers make sure you get all the information you need in the game, through menus and the HUD.
- Networking
-- The programmers here make sure you can talk to other players and play in the same game.
- Tools
-- As games are becoming bigger and bigger studios need ways to store, create and use mass amounts of data. So you will have a few programmers that make tools for the designers to make all the content for the game, such as a level editor. They will also make tools for 3rd party applications such as 3ds Max, so you can use models in the editor.
The list goes on and on. If this sorta thing interests you I suggest you look up some examples of C/C++ code. If you have good problem-solving skills programming may be for you.
Artists
Well its pretty obvious what they do, they make all the art for the game, but this comes under various areas of development. So heres a list of all of the different areas of Art used in games.
- 3D Modellers
-- Here you have a team of modellers that work on a lot of the content for the game, for example character models, or environment models which are for example a building.
- Texture Artists
-- This branch you have artists that make all the pretty colours on models or anything in the world really.
- Animation Riggers
-- This is more technical than artistic, as these guys will make the 3D models move in game, usually via motion capture.
- Music/SFX Composers
-- These guys make all the sounds in the game, be it music or sound effects, sometimes they might be hired.
- Concept Artists
-- These guys are used in the design process, usually a designer will come up with an idea for an environment and its up to the concept artists to make a visual representation of that.
So theres a quick overview of various jobs in the gaming industry any other questions just ask away
