If you have been granted access to a college shared mailbox you access this through your college email OWA login
Login into your college email using any web browser, then click on your name in the top right hand corner and select 'Open another mailbox...' from the drop down list
Then type the name of the shared mailbox and then click on the search contacts button
Then click on 'Open'
If you get an error then you either do not have permission to open this mailbox or the mailbox is not available, in either case please contact the helpdesk