First of all, what are mods?
"Mod" is short for "modification," and it's an alteration of the original game. In gaming in general, a mod can be as small as a change in the number of something required to fulfill a goal or as large as an entire new game, but for LDW games, mods are always simple changes in the game's appearance.
If you browse
the Game Mods section of the forum, you can see a variety of different kinds of mods for LDW games, from new pots for the plants in
Plant Tycoon to easier-to-find collectables for the Virtual Families games to making the Virtual Villagers Christmas-themed.
Second of all, how do you make mods?
Making mods for other games can require quite a lot of know-how -- I've made mods for
The Witcher that took a thousand hours to make -- but mods for LDW games are very simple and only need a simple image-editing program, like Photoshop or Gimp.
Thirdly, do you need a computer to handle mods?
Almost all mods are made for computer games; modding games on other platforms ranges from horribly difficult to completely impossible. It's one of the reasons why I prefer computer games, because you can tweak those to your liking.
LDW games are small and simple enough that mods for LDW games are hosted here, in
the Game Mods section of the LDW forum.