Keycloak permission to restrict account based resources

In our existing customer portal using our own permission system, we can set an account "context" to an user with the permission to only able to action on any resources in certain accounts.

How do I do that in Keycloak?

I am a bit confused reading the roles, resources, policies and permissions, I tried reading this stackoverflow Resources, scopes, permissions and policies in keycloak but it doesn’t seem to directly answer my question.