Backing up a server

Hello,

I am new to servers and I do not have any experience at all.

I would like to know if I can just connect an external HD to my Server (currently running Windows Server 2003) an make a copy-paste action to copy the files and have a back-up? Is this process risky (I need to copy 1TB) ? or do I need any special sequence that I must follow to get the back up of these files? 

Thanks!