Arma Reforger

Don't be intimidated by the low completion percentage, this achievement is very easy, however it is time consuming (1 hour, or 1 and a half hours if you crash provided vehicles, because there is no replacements, forcing you to walk) You will learn everything that you need to know about the game in this game tutorial, it is very well described by the narrator, and is fun to complete if you like realistic games. You simply need to complete all 10 training courses. I don't know if you can complete them in multiple sessions, but I would go ahead and do it in one go. The courses are:

Infantry Basics (1st section):
Movement (2-4 minutes)
Firing Range (5 minutes)
First Aid Course (5-7 Minutes)
Map Reading (10 minutes if you don't crash, 30 minutes if you do)

Vehicles & Logistics (2nd Section):
Basic Driving (5 Minutes)
Helicopter Basics (5 minutes if you land good the first time)
Advanced Driving (7 minutes)

Advanced Combat (3rd and Final Section):
Base Tour (5 Minutes, you must walk up to all of the yellow arrows, then return to base with the radio)
Building Support Structures (6-7 Minutes)
Capturing Objectives (12 minutes)

I will be making guides on the other achievements as well, because currently there are not any posted.