First, have you ever done a full backup?
If not, that's the very first thing you need to do. And do it right now.
Then backup the transaction log.
It's very easy to do, you can find the syntax in the Books OnLine (BOL). The BOL is installed as part of the Client Tools and can be found at Start>Programs>Microsoft SQL Server>Books OnLine. Use the Index tab and enter BACKUP DATABASE. The other command you will need is BACKUP LOG.
Both can be done while the database is operational.
-SQLBill