Step 1 = pick the mission to build a Harvest drone
Step 2 = follow the yellow mission arrow to the green crystal
Step 3= harvest the green crystals
step 4= refine the green crystals
step 5= put 2 refined green crystals in a Level 2 fabricator
step 6= put the Harvester drone on the ground
Should now clear the mission
That is suppose to be the way to do the mission....however....
I have found that you can use any green crystals from the game as long as you harvest it & as long as the mission is available to you..... you don't even have to have picked the mission...just wait for the prompt box (the one that is located middle bottom) to tell you what to do once you have picked up any raw green crystals
You can do the same thing with making a "Guard Drone" except you will be using the brown crystals.