On Macs, the font size is usually handled by each individual application instead of by the system. However, if the application uses the default font sizes (rare), Tinkertool can change those:
http://bresink.de/osx/TinkerTool.html
Additionally, the key combination of COMMAND+SHIFT+PLUS SIGN (+) will "zoom" inside almost all applications, and COMMAND+SHIFT+MINUS SIGN (-) to go back down.
What kind of mouse do you have? If you're using a trackpad you can also "pinch to zoom", if you're familiar with that. Place two fingers down on the center of the trackpad and move them apart. Squeeze back together to un-zoom.
Side-note to your question, since I mentioned keyboard shortcuts: It's quite common for advanced Mac users to utilize a number of keyboard commands instead of the mouse.
There's a list of them here:
http://support.apple.com/kb/ht1343
I use OPTION+COMMAND+EJECT all the time, as one example, to put the machine to sleep.
They take a while to get used to, but they're a lot faster than reaching for the mouse or trackpad.
Change desk top back ground.
Go to System Preferences, then into Desktop & Screen Saver. Once in there, make sure you're on the Desktop tab at the top of the screen, then you'll see a Finder on the left where you can select from a number of pre-loaded Apple-provided images, or go to "Folders" and add a Folder of your own (for rotating images) or Solid Colors, etc.
Computer illiterate has more computer than he can handle.
Not a problem for someone who knows they're in over their head and willing to learn a few new tricks.
There's some good basic videos on various things that help new Mac users quite a bit here:
http://www.apple.com/findouthow/mac/
Holler if you need more help...