Google this shit fool. There's hella help out there, but anyways..
RAM stands for Random Access Memory. It's what's used when you run applications. Applications are programs like Internet Explorer, Windows Media Player, Your antivirus, etc
Hard drive space is the amount of storage for your computer, how much data it can hold.
1000 MB = 1 GB
The more space you have, the more shit you can put in your hard drive.