advice: search beamng on your steam press manage user folder open it and click "open in explorer" now once you opened it you will see your things click mods here: now paste the file in there and you will have it in --- Post updated --- ps: on some mods they dont work so for those mods click the mod and you will see vehicles copy the vehicles folder now repeat after me press "steamlibrary" "steamapps" "common" "beamng" and paste it keep in mind you will find this in your hard drive ps: if it does not have a vehicles folder create a new folder name it vehicles put the thing that it was before in the vehicles folder now once its done put the zip in the mods folder some mods have rar files but you can either find the zip or just vehicles now put the vehicles in the hard drive with "steamlibrary" "steamapps" "common" "beamng" and paste it
