Composing music for games ia an enormous topic and I don't think it can be adequately summed up in a single tutorial doing any justice to it. I suggest you start by making music that you enjoy making and see where you go from there. I wrote a bit about the role of music and sounds in a game, but that's more for a developer's point of view. As far as learning to write music for games, that's an enormously long endeavour that includes tons of practice, research, listening, and slow improvement.
If you already have a few years of writing music behind you and want to get music IN games, that's another story. I recommend putting your music on NG first off, using the collabinator, participating in contests and being active in the NGAP community, and doing every game jam you can find on the internet. Just be careful about people asking you to do large amounts of work for free. Remember: regardless of how good or bad you are, your time is valuable. :)
Sounds is a bit different of a topic. Sound design requires a good ear and a willingness to explore and combine sounds at will. I suggest you mosey on over to freesound.org or open up some synths and filters in your DAW, come up with an imaginary "shopping list" of sounds you want to make (e.g. dinosaur stomp, bow twang, orc roar, etc.) and see what you can do with the sounds you can find and manipulate to get the effect you need. Sometimes you have to combine dozens of sounds or have massive chains of filters just to get the "right" sound.