Open Enterprise Manager and expand the registered SQL Server

Expand Databases

Right-click on the database that you want to backup, select All Tasks -> Backup Database

If you would like to make a complete backup (recommended), make sure "Database-complete" is selected

Click the Add… button

In the File Name field, select the directory and type the name of the backup file you would like to create.

Click OK

Click OK again, and your database will be backed up.