See the Apple up in the upper left corner. Click on that & come down one menu item to "About This Mac" & up pops the info on yer GB of RAM. If you click on the 'More Info..." button on that same window, then you'll see 'Hardware' listed with a little white triangle right next to it.
You can click on that & it'll point sideways or downwards... then if you select memory it will give you all the technical info about said RAM.
But if you want to know how many GBs of available disc space you have; then go to your Utilities folder in your Applications folder and open Activity Monitor. Click on "Disk Usage" and you'll see Space free. No not outerspace, silly, but it really is free or let's just say it's "available" as Chris mentioned.
So there you go, myragirl...
Peace Out
mm~