Google would have answered your questions here.

Unity can be programmed in either of the following:

• Unityscript. Modified form of javascript. Infact it is more or less javascript running on mono/.net. Javascript is usually used alongside HTML for writing extra functionality into web pages like rollover buttons and this very text box that I am typing this post in.
  
• C#. General purpose language. Increasingly popular for desktop based software.
  
• Boo. Pretty cool .net language with python-like syntax. Incredibly simple description would be a mix of C# and python. Also has a few features from some other languages.
  

Of the 3 your best off with either unityscript or C#. Most docs are in one or the other. Which you choose is upto you. If you prefer the idea of web technologies over the desktop then maybe unityscript is for you seeming as it is close to javascript. If you have interest in writing desktop programs as well though then C# might be the way forwards.

Unity is more orientated towards working in 3d. 2d can be done but they don't really offer any support for it.

Writing a game is a bad idea for a complete programming newcomer though.

I took a look at Unity when I was trying to figure out where to start a couple of months ago. It's a great game engine, but I wouldn't recommend it to a new programmer.

If you're just doing it for fun, check out Construct2. It's a pretty cool HTML5 game engine with a lot of built in features you would normally have to code into a game yourself. Check it out and see if it's for you.

Spriter's Resource will get you started with some game sprites, but you can find more through Google. Just search for "free sprites", "free game sprites", and "free tilesets".

If you are using Unity, it's known for its asset store, which has pretty much everything, definitely sprites.

Unity is a great way to make money. Most of the developers, however, are very lazy, and annoy me. The only serious developers are people developing tools, because *almost* everyone on the forum constantly quits games and spends a small amount of time on everything. If you look at the asset store, many expensive products that many people buy (Like the guns tool, for example) have *very* little coding, that is extremely simple, and yet the people behind them get lots of money. It annoyed me to no end when I used Unity that everyone I talked to on the forum seemed to not care about their projects and were pretty lazy. The forum is also filled with 10-12 year old's talking about they're new MMORPGFPSRTSTD Game that is going to be their first game.

I highly respect the people developing tools (Like the RPG tool / MMORPG tool) because they are insane. They are amazing programmers who know the ins and outs of Unity. I love how they make money doing what they love and how they help so many newer developers. I look up to them highly. Now, there are many tools developers that I half-like. The person behind the FPS kit (I forget what it's really called) annoys me, because he makes so much money from it and helps so many new developers, yet I could probably code it in a day if I sat down. I also understand that he didn't have much time to work on it, etc., so please don't get mad at me. It's more jealousy than anything else.

I never made a game with Unity. The community annoyed me, so I learned C++ and started hard-coding my games. If I went back to Unity, my new experience with coding and hard work would probably make even my first few games far better than more than half of the "projects" other people are working on.

for 2d game you can use cocos2dx but for 3d game unity3d better .