1. Go to the Twitter website and sign in. If you don't already have an account, read up on how to join Twitter.
2. If you already have the web address of the person you want to follow, navigate to it and click on the Follow button under their name.
3. If you don't already have the address, click on the Find People link at the top of the page.
4. You can find people by typing in their username or their real name and searching for them. Once you have located them in the list, simply click on the follow button.
5. If you have Yahoo mail, Gmail, Hotmail, AOL mail or MSN mail, you can have Twitter search through your email address book to find people you know. Just click on the "Find on other networks" tab, choose the service you use for email, and type in your credentials.
6. If you are on someone's page and you want to follow them, simply click on the Follow button below their name.
7. Following people that are following you is also very easy. On the right side of the page, Twitter gives your follow stats. Just click on the "followers" link in the middle column. This will list everyone that is following you. To follow them back, just click on the 'Follow' button.
Source: http://webtrends.about.com/od/howtoguides/ht/how-to-follow-people-on-Twitter.htm
