There is a help page on every UnionCloud website at www.yourdomain.com/help 

This page includes the following links: 

1. Didn't receive activation instructions? 
2. Didn't receove unlock instructions? 

You can point students to this URL for them to find out help on signing in. 

Registration and account help

You can edit all of these questions in the backend dashboard under Admin > Setup > Messages and Emails > Registration Help.