Note:  This is just something I did for myself. I am sharing it with the community. I do not represent Atavism and it is not an official implementation of UMA.
1. Start a new project. I implemented this in Atavism 2.7.d. It may work in 2.6 or 2.7.e but I haven't tested those versions.
2. Next Import UMA from the Unity Asset store. This must me imported before step 3.
3. Import the package I attached to the forums.
4. Add Scenes to the Build Settings: Login, CharacterSelection, MainWorld. Save Mainworld when it prompts. Not sure why but it fixes a bug in 2.7.d when first entering the game. This is not related to UMA.
The CharacterSelection scene will be self explanatory for creating a character.
This folder contains examples for UMA wielded items and UMA armor.

Drag armor prefabs here like any other armor prefab:

7. Drag Wielded Item prefabs here like any other armor prefab:

If you select a prefab in the EquipmentDisplay/UMA folder and highlight the "Mystic Robe (UMA)" prefab you'll see something like this. Select "Armor" for Equipment Type and add recipes for Human Male and Human Female (both are required). If new races are added you will need to add slots for them as well. 

If you select a prefab in the EquipmentDisplay/UMA folder and highlight the "Knight Sword" )" prefab you'll see something like this. The position and rotation can be adjusted so that the item sits where you want it on the character socket. If you want to use Rest Sockets then you will need to adjust position and rotation for both Human Male and Human Female and any other races that you add. You'll need to do this for every wielded item that you add to the game.

If you do not want to use Rest Sockets then you can disable them by unchecking "Use Rest Sockets" on the uma_receiver prefab. The uma_receiver prefab is located in the Resources folder.

To add UMA NPC's go to the "UMA NPCs" folder. You can make a copy of the Uma_Merchant_Knight using CTRL-D and rename it.

Next run the "UmaNpcAppearance" Scene from the editor.

 Select "AtavismUmaNpcAppearanceCreator" in the Hierarchy.

Then drag your UMA NPC here. Create the Appearance you want and Click Save To NPC.

Add your UMA NPC like this: