How do you backup an SQL Server Database to a Network Share?
Assuming that the SQL Server Service you're using has access to the network location, you can see a hands-on example of how to backup to a network share in either of the following, free, videos:
Backups with SQL Server Enterprise Manager
Backups with SQL Server Management Studio
This video also provides some information on other options and some caveats about backing up to network shares:
SQL Server Backup Best Practices