Login to Office.com with your school email address and password.
You will be faced with the page below, which is the the front page for Office 365.
Locate to the SharePoint app that I have highlighted in yellow.
When in SharePoint you will be faced with the below screenshot, yours may look a bit different as yours might be blank and might not have any sites yet.
If you don't have any sites you can search for some up in the search box at the top that I have highlighted yellow.
Once you have been on a SharePoint site when you close it down, you will see it under Recent, you can also press the little star next to the Recent SharePoint you have just opened to save it to Recent.