Google Takeout Overview
You should not transfer data from your Tigermail account until after you are done accessing it for school. There is a two semester window between your last class and the account being disabled. Once you are done taking classes it is recommended that you use Google Takeout to transfer (or download) your email and documents.
Here is a tutorial that will help explain the process in greater detail: https://www.youtube.com/watch?v=iBXet3by4SU