BeamNG Drive does not have a built-in multiplayer feature at the moment, but there are mods available that allow you to play with friends. One popular mod is called BeamMP, and the following is a brief tutorial on how to install it.
Step 1
Download the "BeamMP_Installer.zip" (Download Client) on www.beammp.com.
Step 2
Unzip the file and run this application to install BeamMP on your computer.
Step 3
Make sure that your game is closed and run the BeamMP launcher. Then BeamNG Drive should start automatically and you will see a multiplayer tab in-game.
Step 4
You must create an account on https://forum.beammp.com and log in to your account ingame. (dont use the "play as a guest" function).
Step 5
Now you can play on BeamMP servers. Make sure to always start your game through the BeamMP launcher, if you want to use multiplayer.
1: When you play on a server, you always have stand still for a few seconds, after another player loaded or modified any type of vehicle. You can just keep driving if you want no lag, but then you wont see the unloaded vehicle of the other player.
2: BeamMP needs a good Pc. Try to keep your settings as low as you can, especially if you are on a low-end setup. Or join a server with a maximum amout of 6 people, for example.
3: There are also server with mods, but keep in mind that this is even more memory intensive.
4: You can also host your own BeamMP server! There are various hosting providers available, but keep in mind that this will usually involve a cost.