1. Log on to http://www.secondlife.com/join/
2. Choose a name. (At present, last names are chosen from a predetermined list.)
3. Enter the other requested information.
4. All that's needed is a valid email address, to confirm you aren't a bot. You can get 250 Linden Dollars if you tell them a valid credit card number, though.
First Basic account is FREE, and includes access to events, shopping, building, scripting- everything you can do in Second Life. After your first free Basic Account, each Additional Basic Account (known in-world as an "alt" account) costs a one-time fee of $9.95.