I am starting to finally figure things out about this game but one thing I don't seem to understand is the Inn. What is it for? How does it work? How do I get it to work? When I click on Buildings, it is grayed out. How do I make it an active building?

I'm assuming the Inn is greyed out because you haven't built it yet? You have to build the Inn like any other building, by either buying (from Item Trades from other players) or finding (on islands) a blueprint , then using this blueprint and then going to Manor -> Craft & Construction to actually buid the Inn. The materials you will be needing you can find here: http://beastkeeper.com/recipes-list

Once you've built it, you need Invites that you may have come across. You use an invite and a guest will arrive at your Inn. This guest will stay for 3 days, give 50s per day and provide certain bonuses. A Trainer will for example half the training fees for pets at Riding Halls, a Geneticist will allow you to research specific genes on pets, not just random ones, a Mammal Catcher will make it easier for your catchers to successfully hunt for mammal creatures (Puma and Unicorn) and so on. Useful in the beginning is a Clairvoyant Invite in my opinion, which lets you see all the pets on the map. As long as you don't have the Cartographer's Guild, this is a VERY useful person to have in your Inn if you want to catch pets from the Wild.

Hope this helped you, if you have more questions, feel free to add to this :)

This was BRILLIANT help!!! Thank you soo much!