
Installation is easy inside Euro Truck Simulator 2. Place both folders inside bin of your ETS2 installation. 

You will now notice that each time ETS2 now starts it prompts the SDK has been activated. 
Unfortunately you have to press OK to this message every time, but it's a small price to pay for the added features that are possible via the SDK.

Adapted from from https://github.com/nlhans/ets2-sdk-plugin and https://github.com/RenCloud/scs-sdk-plugin

Operations are the same for American Truck Simulator