Registering for a free Zotero account gives you a number of benefits, including the ability to sync your library between computers and Zotero's web servers, participate on the Zotero forums, and create and participate in shared Zotero groups. To create an account:

1. Go to www.zotero.org/user/register.
2. Provide a username, email address, & password. 
3. Follow the instructions provided in the resulting confirmation e-mail to activate your account.

When you have completed creating your Zotero account, see Syncing Your Library to sync your source data to zotero.org.