You need an external hard drive that is either accessed via USB or over wifi.
Since you're not a tech minded person, I'd go with Time Machine. Go to Best Buy or wherever you buy computer accessories (not the Apple Store; you'll be paying WAY too much). I'd suggest a drive made by Western Digital like a My Passport or My Book. Get a size that will fit your internal drive plus some. 500gb should be plenty if you have a newer MacBook Pro. You also don't need the Mac-specific ones. You'll format it properly once you connect the drive.
In order to set it up, I'd go to an Apple Store or authorized service provider and get some help or find a friend who has some familiarity with Mac. I can try to explain it to you, but it is a but tricky if you don't know what you're doing.
An easier but more pricy option is to buy an Apple Time Capsule. It should come already formatted correctly, and it connects over wifi.
Time Machine itself is pretty easy. Find the clock icon on the right side of the menu bar. Click it. A window opens. Just slide the bar to On and set up from there (if I'm recalling from memory correctly; I'm too lazy to dig out my Mac, and my time machine drive isn't with me).