First, read this question:

Second, there are so many musicians and sound designers of all skill levels (and expecting various degrees of compensation from free to standard rates) wanting to join on with a project. If you’re having trouble finding somebody, you just need to find more internets. ModDB, GameDev.net, forums for specific engines/tools that have tried to form a general game development community. Seriously consider giving working with somebody a shot. You’ll both learn a lot.

If you’re wanting to be a one-man developer, then you can take a sound editor, microphone, and samples and synths, and now you’re a sound guy. It’s another art/craft to learn, no different in that regard to drawing/modeling/other-graphic-art, game design, and programming. Use the tools Valryon mentioned (SFXR and Audacity) to get started. Also look into:

• Wavosaur – A freeware sound editor
• Reaper – A very inexpensive DAW (digital audio workstation, used for producing music from audio recordings and midi) and Ardour, a FOSS alternative for Linux and OS X
• KVRAudio.com for free basic VSTs (often playable directly in Reaper and other DAWs
• Modplug, Renoise, SunVox, and Buzz are music trackers for old-school-style game music composition
• Links for the lazy: Audacity and SFXR

For learning about sound, you should be aware of some of its physical properties and how we are able to digitally represent it.

To start making music, you should learn about music theory and how to produce music.