This is fairly easy to unlock very early in the game. Through natural progression you'll get it around the time you get the T45 Power Armor. (i won't be spoilering here)
You gain EXP from killing things (animal, raiders,...), exploring, building/modifying weapons/armor, building settlements, hacking terminals and completing quests.
No need to actually spend the perk points. Some Achievements ind FO4 pop silently, so check the achivements app if needed.