To the best of my knowledge, DraftKings does not have an "official", well-documented public-facing API.
Instead, they have various HTTP endpoints that do not require authentication (so are "public" in this manner).
These "public" endpoints allow one to fetch data for various resources including contests for a specific sport, or players that are draftable for a given contest (as well as relevant metadata).
As DraftKings makes no guarantees about it's "public" API, this client makes no guarantees that the existing API methods will work consistently.
For documentation about package installation as well as the client's API, please see the documentation site.