Lots of guides have lots of good info. I compiled all of the basic info to get you started, leaving out all of the extras and big lists, that just clutter your brain. For more info, you can visit the guides I used as references. They are all quite excellent!
- The Grumpy Elf’s guide to Garrison Achievements, including ones that unlock blueprints. Also some really good FAQs, and a really thorough guide to each building (with and without having that profession).
- Vittoriya WoW’s guide to followers (missions, abilities, etc)
- Warcraft Pets garrison guide for pets (and a guide for the elekk plushie from MurlocHarbor)
- Denizly’s garrison guide on mmo-champion and Icy-Veins (including info about followers, outposts, and more)
- Alternative Chat and a podcast episode all about Garrisons
- Garrison management addon
- Twitter friends who helped: @Malvenue, @VittoriyaWoW, @yoco68