These are all valid questions to ask about your computer, especially if you're trying to get the most out of it. If you'd like to know the statistics of your computer at any given time then there is a super neat application out there called iStat Menus that can help with just that.
iStat Menus lives in your Mac's Menu Bar (near the Date & Time at the top of your display). It consists of seven different reporting modules that measure all sorts of performance specs of your computer. Its customization options also allow you to choose which reporting modules appear on your menu bar.
For example, if you're noticing that your computer is running slow and you want to know if getting a RAM upgrade will make it faster, then you can use the RAM reporting module to show you how much of your available RAM you're using at any given time. If the RAM icon fills up while you're working, then that's good sign that upgrading the RAM will speed things up.
I personally like the custom date & time module because you can click on it and have a mini-calendar appear. (So you don't have to launch your calendar application to quickly see a date in the future.)
Give it a whirl, it's free, and donations are also accepted.
Are you already using iStat Menus? What modules to you use the most? If you have questions, leave 'em below!