Go to portal.office.com and login with your school email address (if you're already logged in to your email, it may take you straight there without having to log in).

Click on the Sharepoint logo on the left-hand navigation bar

When the Sharepoint page loads, click on the group you want to sync. In this case, we're going to sync the "MJHS School Supply List" group. 

When the group opens, click on the Documents link on the left. When the documents page loads, there is a Sync button in the center of the top settings bar. Click it, and it will walk you through syncing the folder to your computer where it will show up in File Explorer.