A wiki belongs to one owner and can be shared with other users at three levels of trust. Permission lives on the wiki itself — there's no per-page or per-block override.
Roles
The owner is implicit and cannot be removed. Other members get one of three roles, ordered by growing capability.
Viewer
Reads. Equivalent to anonymous browsing on a public wiki, but with access to a private one.
Editor
Reads and writes content — pages and blocks. Cannot change wiki settings or manage other members.
Admin
Everything an editor does, plus changes the wiki's title, visibility, and language, and manages members. The closest thing to a deputy owner.
Adding and removing members
Open the gear icon (Manage) on the wiki. The Members section lists everyone with a role. Click "+ Add", search the user's display name, pick a role, confirm. To change a role later, click the current role next to the member and select a new one. "Remove" revokes their access entirely.
Users you invite must already have a Wikilayer account — email invites aren't supported yet.
How visibility fits in
Permissions answer who can do what. Visibility (Three flavors) answers who can see the wiki at all. A public wiki is readable by anyone, members or not; a private one is invisible outside the member list. Archive hides the wiki everywhere except the owner's /manage.