What is the Manage Permissions page for, if I set access in Manage Roles?

No. Manage Permissions is a read-only reference list. It shows every area of the admin that a role can be given access to, with its Group, Module and the Plugin it belongs to (or "core"). There is nothing to edit there.

Access is set in Manage Roles:

1. Click Permissions on a role's row.
2. For each module, tick view, create, edit and delete separately, so a role can see orders without being able to delete them. The all box at the top of a column ticks that action for every module.
3. Click Save role.

Modules that belong to a plugin are tagged with the plugin's name. The Roles & Permissions menu only appears if your plan includes staff accounts.