Mods stands for 'modifications'. Since you are using Windows you'll be able to use them (iOS and Android users can't as they are unable to access the file system). That is assuming you have downloaded the game from this site; some portal sites prevent access to the files.

The VF2 mods forum contains some user-created mods. Before starting, make sure you read the installation instructions thread. In particular, make sure that files are backed up before installing!

If you have any knowledge of image editing you might be able to create your own mods; there are general instructions in the mods forum. If you do create a mod, why not upload it here for others to enjoy? The posting guidelines are here.