Battle of the Bands is 100% free to join and use. To start register for an account on this page. After you complete registration you will be sent an email to verify your account.
Click the link or copy and paste it into your browser window. After this your account will be verified and you will be able to login.
Once logged in you can choose what current battles you want to join. By clicking join you will effectively join the battle, and it's time to start promoting your newly created page.