Buying/acquiring domain names
You can always buy a domain name from its owner or wait for an existing domain to expire (so-called dropped domains). For dropped domains, there are a host of online services that, for a fee, will help you navigate the increasingly complex world of expired domains. This approach will yield some inevitable frustrations: the system is dominated by experts that have mastered its subtleties. As a newcomer, you'll likely have to endure a learning curve. Also, an owner of an expired domain is entitled to a redemption period during which, you'll have to wait if you want to snatch up a choice domain. For most SEO pros, the extra time and risk isn't worth it—especially when you can overcome a less-than perfect domain name with sound on-page optimization and some extra linking power.
You can also buy a domain in the aftermarket from an existing domain owner. Dangers to watch out for with this approach are that some domain owners make it impossible...