How to assign users to groups

Edit: This page should help.

I recently installed Discourse 2.6.0.beta1 on Ubuntu using the DigitalOcean One-Click image. It seems great, but I’m not seeing how to add a member to the Moderator group or Staff group. For those groups, there is no such button.

Admins should always be able to add members to any group, right?

I notice that I’m listed as “Owner” of these groups in the multi-tile Groups view. (There is a green “Owner (shield icon)”.) That should also let me add members to the group, right?

What might I have done wrong?