"1) Suscribe to a mod through the Workshop.
2) Go into the workshop folder of the game (see picture)
3) Localise the .CMS file and copy the name (minus the "car_")
4) Go into the Car folder of the game (Car Mechanic Simulator 2018\cms2018_Data\StreamingAssets\Cars) and create a folder with the name you've copied in step 3
5) Copy the "Liveries" folder inside of the workshop mod inside of the newly created folder -OR- create a "Liveries" folder and put your liveries in it."