If you receive a link to Analytics data, for example, to a report or dashboard, and you don't have access to the account, you can request access.
When you click the link, then click Request access to send an email request to administrators of the Analytics account. One of those administrators can grant you access with the Viewer role.
Once you have access to the account, you can open Admin, and click User Management in the Account column to request additional permissions.
If you are an Analytics administrator with the Administrator role, you will receive an email with the access request.