if you want to work in videogame art, it's best if you learn a technical skill like modeling, texturing, shader-writing, etc.
just being a concept artist is really fucking difficult, because there are a lot of very skilled people out there and not that many jobs. but the more technical stuff you know, the more valuable you are and therefore the more employable.
I know people who work in this field, one of them kept poking me to do concept art for him but it always involved 'ok, I want a picture of a helicopter...' which I am not even remotely interested in drawing.
What an artist does is...whatever needs to be done. It depends on you, the company, all sorts of other factors.
Most game companies don't have a big building you come into every day. For the most part, you will be working from a distance, communicating via email, chat, etc. Many games are made by a few guys in the garage.
Work is generally going to be pretty freelance. You may get hired for a job or a certain amount of time. Only very large companies are going to keep a permanent staff of artists.
There are basically two kinds of art for the games (excluding the rendering and stuff) and those are the designs and the promotional art. Designs are deciding how something should look and depicting it accurately for the people who render it. This includes characters, backgrounds, levels, etc.
The other kind of art is promotional- the kind of pictures you see on the game box, website, posters, etc.
You need about 15 pieces of art. You should focus on what you want to do- if you want to do characters and costumes make sure there are lots of those in there, if you want to do backgrounds put those in, etc. But you will get hired based off of your portfolio, and they assume that what you put in there is what you want to do. Yes, you need to be able to do a variety of things, but if you don't want to be drawing backgrounds all day then don't make that the focus of your portfolio.
Yes it is hard to get into. But once your actually in and settled, you can make money off it to not worry to pay the bills.
One artist field is Visual development or Concept art. You could also be the animator and 3D modeler. Or layout the maps. Look at any that is visual, and there is a designer for that. Sometimes, you could also be a spriter (or making video games sprites) too.
You also need to do alot of good paintings, not anime or manga characters sadly, and you need to prove that you can draw flawlessly. Its very demanding, because basically as a concept artist, your basically developing the stuff that goes into the game.
There is a ton of resources you can look up. Ctrl-Paint, Fengzhu Designs, Conceptart.org, CG-Society, matt painting, my teacher Chris Legspi, ArtGerm, etc.
And yep, its a good idea to look up the jobs and doing alot of research your self. You probably can get more information then me.
You would do stuff like character designs, backgrounds, interface design, and building 3D models of characters. It's extremely competitive and hard to get into. And apparently you need to be very committed and often work overtime. Unless you are working in an Indie studio, you are not always going to be completely designing and creating your own ideas. Your studio might be working on a chain game like a spongebob or Barbie game.
It's a good idea to check out what the game industry is like in your city. (The big studio s in my city shut down recently and it's all indie now.)