Just go to the link provided by Wednesday. You will be able to see what all the different kinds of mods are. A mod to make skills easier to max is an XML Tuning Mod (the easiest kind of mod to make, which requires no programming). You will find that under the General Modding section at the site Wednesday linked to.
ETA: It's great to go to ModTheSims to find out how to make mods. There are many tutorials, FAQs and threads dedicated to people who want to learn to make mods. If there's something you don't understand, you can ask there.