What is matching RAM?

It depends on how specific you are about speed matching, and any potential problems. if you want it to work correctly and not have a problem you will want to match the modules exactly. If you just want the speed to match, you can buy a module of the same speed and match the speeds. These 2 options are what I suggest doing.

If you aren't concerned about any of that and just want to get more memory, you can mix and match speeds and brands as long as you are okay with the new module taking the speed of the original module(s) that came with the computer. I don't suggest doing this but it is an option. The problem is doing this can cause instability problems. It doesn't always happen but the chance of a problem isn't exactly in your favor. It's better to match the speed if you can, or bite the bullet and buy all new memory modules. With that out of the way, here's the guide to install the memory in the system.