This mod allows you to add your own compatibility with other mods. Lets say you downloaded a mod that adds flying saucers... but wait, there's no "flying saucer" option in the mod! You get in, fire your weapons and you notice that despite having every vehicle class enabled, you still didn't get your ammo back. Fortunately you can easily fix that.

To discover the category of your vehicle mod, enable Debug Messages on the mod settings page and get in the vehicle you wish to enable to mod on.

The mod will tell you the category, in all caps, of the vehicle you just got in. This will only happen if the mod didn't recognise the vehicle, or its category is disabled!

Remember the vehicle's category and write it down in the Compatibility box on the "Misc" category. So, if you get "ALIENMOD_FLYINGSAUCERS" from the debug message you'll write down "alienmod_flyingsaucers" (without quotes) in the box. it is case insensitive. If you have multiple categories, you can separate them with comma and space. Your compatibility box will look like this (without quotes):
"alienmod_flyingsaucers, mymod_vehicles_mechs, metalgears_bipedals"

Make sure that the "Compatibility - Toggle" option is checked. Otherwise, the mod will ignore the categories listed by you. Alternatively, enable "All Vehicles". This will make the mod allow and apply to any vehicle. This is particularly useful if you have many, many mods with multiple new categories.

Post here if you still have doubts.