This is awful, it doesnt give any real world examples, and it jumps to the next screen having miraculously setup the openAPI resource.
I have been complaining about poor documentation ofr 2 years now, nothing has improved and retool isn't an insignificant cost to our company
Thanks for the feedback, @peter.b. 
In this particular case, it looks like the page you've linked does have all the necessary details for configuring the resource, but very little of it is actually demonstrated via the embedded tutorial. Part of the reasoning here is that the specifics differ between cloud and self-hosted deployments, but I agree that it could be improved.
I'll pass this on to the owning team.