Yes, documentation is currently lacking, sorry. The focus has been on getting things functional for all the game toolkits, but documentation will come.
Have you looked at the Unity example projects? Basically there are these pieces:
Material asset: this has the image from the texture packer and the shader set to Skeleton.
Atlas asset: has the Material asset and an atlas file from the texture packer.
SkeletonData asset: has the Atlas asset and the JSON from Spine.
SkeletonAnimation component: added to a GameObject to draw the Spine animation, has the SkeletonData asset.
So, set up your Material, Atlas, and SkeletonData assets (use Assets -> Create menu to create them), then create a GameObject and add a SkeletonAnimation component to it. If you have trouble or other questions, feel free to ask them here.