Auto Actions Trigger List and Descriptions

The trigger list on the Auto Actions plugin is very long and sometimes I don't know what each does.

For example whats the difference between "After User Update" and "After Update User"?

Is there a list with descriptions of what each trigger does?

I'm trying to change usergroups for a user based on a profile field being updated and being triggered on the saving of the profile (whether it be by the user or the moderator). Which trigger do I use?

For example whats the difference between "After User Update" and "After Update User"?

onAfterUserUpdate is frontend user edit save and onAfterUpdateUser is backend user edit save.

Is there a list with descriptions of what each trigger does?

Nope, not at this time. For the most part they're self explanatory. For example after user update is after the user has updated. After update user is after updating a user. All the new triggers are a little more specific though, but some of the older triggers may still be a little vague.

I'm trying to change usergroups for a user based on a profile field being updated and being triggered on the saving of the profile (whether it be by the user or the moderator). Which trigger do I use?

Both onAfterUserUpdate and onAfterUpdateUser.

Is there a way to access this action via the manual URL (link), and specify the user in the URL? Or do I need to create a separate action for this?

I'm trying to have the following:

1. user change this field via their profile
2. moderator change it for user via user's profile update
3. user execute via a link anywhere on the CMS
4. moderator execute (on user's profile) via a link anywhere on the CMS

Do I need to create separate actions, or can I use the same action?

Is there a way to access this action via the manual URL (link), and specify the user in the URL?

Only if Triggers is set to None. You can then specify &users=USER_ID. Note &users= can accept a comma separated list of user ids if you want to send more than 1.

Do I need to create separate actions, or can I use the same action?

Yes, you need separate actions as you can't directly access an action without Triggers being set to None. Allowing direct access to an action with triggers causes the action to be unable to know what to expect. I don't recommend you directly change a users field with a URL unless you've safely secured. To do that you need 3 actions. 1 is acting on the triggers, 1 accepts &user= and has access set to Super Users or something only moderators have, and 1 has User set to User so it always acts on the viewing user (this one the enduser would click).

Can I use the username (or other custom fields) instead of the &users=USER_ID ?

No, the URL can only accept User ID. You can then use any substitutions you want inside your action it self like username, etc..