To make all of the below somewhat concrete, it may be best to start with the early 2024 demo recording and the in-repository demos under endo.
Object capabilities
What are capabilities?See also: https://en.wikipedia.org/wiki/Object-capability_model
https://en.wikipedia.org/wiki/Access-control_list
It's useful to recall what ACLs are and how they work.
"ACLs" or "Access Control Lists" being the dominant permissioning model in software since at least Unix.