Download the mod file from a trusted source
Open BeamNG.drive
Go to the main menu
Open the Repository or Mods section
Click Open Mods Folder
Copy the mod file into the mods folder
If the mod is a ZIP file, keep it zipped unless the mod instructions say otherwise
If the mod is a ZIP or JBEAM package, place it directly in the mods folder
Restart BeamNG.drive
Open the Mods Manager in the game
Enable the mod if it is not already active
Load a map or vehicle that uses the mod
Check that the mod appears and works correctly