should i put a [ ] like [student] in the value and label boxes?
You don't need to put brackets in the values. For student just have it be "student" (without quotes). Your issue is the conditions. You're conditioning multiple times the same field. You currently have the below configured
cb_usertype Equal To [Students]
AND
cb_usertype Equal To [Parents]
AND
cb_usertype Equal To [Tutors]
OR
cb_usertype Equal To [Coaches / Instructors]
That doesn't make any sense. You can't have an AND condition against a field that can only have 1 value. You are trying to put all of this in a single auto action. You can't do that. You need to have 1 auto action per usergroup assignment. So you'd have the below.
Auto Action 1
Global
Triggers: onAfterUserRegistration, onAfterNewUser, onAfterUserUpdate, onAfterUpdateUser (covers frontend/backend registration/edit)
Type : Usergroup
User: Automatic
Access: All Non-Moderators (we don't want moderators accidentally losing their usergroups)
Conditions
cb_usertype Equal To [Students]
Action
Mode: Replace Usergroups
Groups: Registered, Students
Auto Action 2
Global
Triggers: onAfterUserRegistration, onAfterNewUser, onAfterUserUpdate, onAfterUpdateUser
Type : Usergroup
User: Automatic
Access: All Non-Moderators
Conditions
cb_usertype Equal To [Parents]
Action
Mode: Replace Usergroups
Groups: Registered, Parents
etc...