If you got any campaign logs before the March 20th '17 update, this is retro-active and will pop on starting up Halo Wars 2.
This is pretty much unmissable when you play the first campaign mission.
There will be these glowing silver 'spheres' around the maps in the campaign. You simply need to drive/walk any unit into them to collect.
In the first mission, there are quite a few and several of them are directly on your path so you will have a hard time missing them!