Warlods of Draenor introduced garrisons to World of Warcraft, with followers who can be sent on special missions to get some extra loot. Not all of them are hard to get, and there are a few really awesome ones who are simply hidden around the map, and you only need to know where to go.
Two videos by YouTuber Opt can help you with that, showing the locations for six of them. You can make them join your garrison easily, without doing long quest chains or heroic dungeons. Followers are probably the most important part of your garrison, so finding these guys is totally worth your time.
Here's how to get Goldmane and Abu'Gar in Nagrand, and Leorajh hidden inside a cave in Arak:
And here's Opt's second video, showing how to find Tormmok and Blook in Frostfire Ridge, and the Image of Archmage Vargoth, who needs a bit extra work, but nothing extremely complicated: