I have reached the limit of my hard drive disk space on my macbook. I am rather computer illiterate and would like to know if there is a way to get more space without getting an external hard drive. I have cleared out as much unnecessary stuff as possible. I know you can add more memory but would that help? What does memory do exactly?

"Memory" refers to RAM, not Hard Drive Space. Try reinstalling Mac OS (with the installation disk included with your computer or, if you upgraded since then, your upgrade disk), and when it asks what you want to install, deselect all languages except the ones you need. This will save a lot of extra space. This frees up a bit of space, and make sure you delete everything that is necessary. If that still doesn’t give you enough space, you can get and replace your old hard drive. You need a 2.5" SATA notebook hard drive found at most hardware stores. You will also need a 2.5" SATA hard drive case that has a usb connector so you can still access you old hard drive. Now is the time to switch hard drives. If you have an aluminum macbook, it is easy. remove the battery cover on the bottom, and remove the hard drive to the left of the battery. If it’s a white or black macbook, it will take a Phillips #0 Screwdriver and a Torx T8 Screwdriver. Open the battery lock (with preferably a coin) and remove the battery. Inside, you should see a metal casing around the inner edge of the macbook with three screws holding it in. Use the Phillips #0 Screwdriver to remove the screws. To the left, there should be a white tab folded in. pull the tab and the hard drive out. Around the original hard drive, should be a case. Remove the case with the Torx T8 Screwdriver and screw it onto the new hard drive. Now put the New hard drive back in and put everything back. Now put the old hard drive into the case, and plug it into the computer. Put your instalation disk into the computer and start it up while pressing "C". Install Mac OS onto your new hard drive, and use the "copy from external hard drive" and select your old hard drive. It will copy everything over. Clear you old hard drive with disk utility by reformatting it, and you get an empty external hard drive.
Hope some of this helps.
from what you are saying there is absolutely no room left on the hard drive, so either you can delete a ton of stuff or buy an external hard drive. Its kind of a sticky issue, because youd have to take off a lot of stuff and put it in the external HD in order to put documents on the macbooks hard drive.
Try and get rid of as much stuff off of the HD as possible, other than that, you will probaly lose a lot of stuff of the computer, although you will still have it in the external HD. Dont bother with the memory unless the mac is slow, memory is Random access memory, basically it takes care of anything you dont save to the HD, like word text and stuff, so dont worry about that unless its slow
memory and hard drive space are 2 totally different things. adding memory will not help you to get more hard drive space.
You have several options.
1: delete files to free up hard drive space.
2: replace the hard drive with a larger one.
3: add an external drive.
Adding more memory could possibly help you with other issues, but will not help with your hard drive space problem.
Memory is what your computer loads programs into from your hard drive to run them. Memory is temporary since it is cleared out whenever you switch your computer off. it has to be reloaded every time you boot your computer from a more permanent storage, mainly your hard drive.
More memory means you can run larger programs or more programs.