Where can I see what actions users of different roles can perform in the system?

You can get an overview of all roles and what actions they are allowed to perform in the system in the organization settings section.

1. Click on the username located in the lower left corner (1), and then click on Permissions (2).

Note:  You need to be an Administrator of the Organization to see this menu.

2. In the workspace level scheme overview, click on the View icon (3).  You will now see the actions that users are able to perform in the different modules, and the roles they are allowed to perform (4).

Also, take a look at this article about the details of permissions.