XP

The best way to describe mods would be something along the lines of free major dlcs that occasionally completely change the game. There are games like the Sims that charge up to 40 bucks for dlcs, whereas there are already hundreds of free mods already available.

Just because it's a mod, doesn't necessarily mean that the quality is any less than the standard of the base game. These mods can add new mechanics, items, characters, designs, enemies, goals, achievements, challenges, and anything else that you can think of.

There are numerous games that benefit from a strong modding community like Minecraft, Teraria, Skyrim, and Garry's Mod. A huge selection of mods definitely increases a game's value.

More mods = more replayability

Over the years, modding has become super easy. Some games even have dedicated software that collect and install the mods for you.

Even just using a massive amount of mods and or attempting to create modpacks will teach you alot about your pc. You will probably also end up spend hours trying to test compatibility.

And then a new game update will be released that destroys any preexisting mods.

So if your game is modded, turn off auto updates and wait a few days before updating. Also try to keep a list of all the mods that might break after an update.