It is a combination of them that you can use at your disposable. It is good practice to specifically call out your authorizations so you can cover your bases. For example, you can specify to deny all unauthorized users, then say allow all others or a subset. The order does matter like aquinas mentioned.
Don't know how to respond you your question about allowing one role but not the other Admin vs user:
ok. Also, if I wish to allow access to only "Admin" role and not
"user" role, adding would work fine, right?
This would work but not as you expect. This would deny all with the "users" role, but then allow for every other role. So to fix this, you would want to add the allow tag with the Admin role specified.