Your task here is to intercept a convoy and capture the artifact. That's nice and vague. You get two infantry and two tank units. Tuck into the dark niche and hide there, getting the first two waves pretty easily. At some point it'll warn you that you have to take the northern road now.

Go straight up the middle, stopping around half way to kill off some enemies. You'll have to be good at getting those infantry in and out of the APC quickly. Head back up the rest of the way north to get the rest of the convoy, and the artifact is pretty much handed to you. This mission is on the easy side. You do learn that the artifact is a Xenofact from Project Garm, whatever a xenofact is.

Ground Control Walkthrough