Log into your Gmail account using the web interface and click on the gear icon located near the top-right of the screen. Select "Settings" from the menu that appears.
Below the word "Settings", click on the "Forwarding and POP/IMAP" subheading. Scroll down to the "IMAP access" setting and click the radio button next to "Enable IMAP".
You will then be prompted to select whether you want your contacts, calendar items, and notes to populate to their respective apps on your Mac. Check the boxes next to each app you would like to use with your SSU account and click "Done"
Your email should now be in the process of saving locally to your machine - this may take a while if you have a particularly large mailbox, so please be patient!