Memory?

Ok, I'm going to admit something here. I don't know a thing about computer memory or backups or any of that stuff. When my main blog was upgraded recently I was so happy to find that it was being backed up. I would hate to think what would happen if I lost it all...I shudder! But how do you know if you need a memory upgrade? Is this something everyone needs? Is it just something business computers need? I'm such a novice at so many computer related things.