When you’re invited to a shared Dropbox file or folder, you’ll receive a notification on dropbox.com, in the Dropbox apps, and over email.
If you’re invited to a shared folder, you can add this folder to your Dropbox account. When you add a shared folder to your account, you have access to that folder and its contents. The shared folder also syncs with other members’ Dropbox accounts. The person who shared the folder with you may have given you either editor or viewer permissions.
Please refer to the following link for instructions.