[Social media "experts" would charge $1,000s for this info, but in the spirit of social media, I am giving it away for free. Please pass it around, and yes, I am appearing in a city near you soon.]
1) Go to http://www.twitter.com/
2) Search for the box that says "Get Started -- Join!"
Deep breath. You're in. Start tweeting to your heart's content.
You'll start to discover a lot of blog posts about which people you should follow? ... should you follow someone if they follow you back? ... is it OK to talk about your brand? ... do a greater amount of followers mean you're popular?
Yes and no on all of the above. The thing about Twitter is you shouldn't follow anyone's specific advice about how to get value from it.
So you only have 10 followers? Are they all loyal customers who buy from you on a regular basis and you like to chat now and again? -- Great! It's working for you!
Do you have BIG FAT ZERO followers, but you follow a load of people? Do you learn something from their tweets about how to make your life, or your business better? -- Great! It's working for you!
"Don't do this." "Don't do that." Blah.