Depending on the type of mod you’ve installed, there are different ways to access them.

Vehicles

Vehicle mods can be access through the vehicle selection menu or through the radial menu.

Browse through the list of vehicles and select the one you’ve installed.

Levels

Installed levels can be accessed through the main menu, under Freeroam.

Scenarios

Once installed, Scenarios will be available in the respective category in the main menu:

UI Apps

Installed UI Apps will be availble from the UI Customization mode, please check this article for more information about UI editing.