"You saved me tons of work"
— Tanner Moushey What They Say

How can we control which users can do certain things?

WordPress lets you add multiple users (go to UsersAdd New) and assign different roles for them. Each role has specific capabilities controlling what the user can and cannot do with in the admin area. Read Roles & Capabilities in the WordPress Codex for full information.

For more sophisticated control than WordPress provides out of the box, such as placing limitations based on post type (e.g. which users can add sermons), you can use a plugin. Here are some options to consider: