When a file or folder in Office 365 is shared with you, you will receive an email like the following:
When you receive such a message - make sure to hover over the Open link before clicking on it - the destination of the link (from our Office 365 system) will always start with https://sunynp.sharepoint.com or https://sunynp-my.sharepoint.com as in the example below:
You should keep this email. The Open link is the way you will access the shared document. You may want to bookmark it in your web browser if it is something you're going to access frequently. Alternatively - you can open your own OneDrive and click "Shared" at the top right. You will see files and folders that were shared with you. Unfortunately - this list can get rather long if you've had a lot of files/folders shared with you.
If you lose the email, the person who shared it with you can reshare the file or folder with you.