When you click on Drive, Google will take into the Drive screen. Here you will not see anything, unless you have already been using Google Drive with this account.
For HERS Online, we will use the Shared drives. If you click on Shared drives, you should see a drive called HERS June Participants. You will use that Drive to access materials and upload assignments. Once the Institute begins, you will also have access to Shared Drives for your Teams. Only people in your Team will have access to the Team Shared Drive.
The rainbow plus sign allows you to create new folders and new documents, sheets, slides, forms, &c. in your drive or in your Shared drive.
You can find out more about Google Drive here and more about Google Shared drives here.
You can also create new a new Google Doc by going to docs.google.com. Here are some directions for creating a document outside of Drive. This is also true for Sheets (spreadsheet) and Slides (presentations).