Go to Settings
Click on "Add Account"
Choose Google as the account type that you want to add
Choose "Existing" as the type of account to create
Type in full GSU email address and password, then click the right arrow
Congratulations! Follow the prompts that follow and choose what you want to sync and you are done and you should start to receive shortly. You may have to wait a few minutes for it to sync depending on how many emails that you have.