Once a Moderator has Invited you, a User, to a Workspace assigned to you within their Portal:
You will receive an email.
In that email is a link you will click which will bring you to the login of the owner's Portal.
During your first login, you will enter your first and last name, and create your password.
The successful first login brings you directly into your assigned Workspace.

Any email notifications you receive moving forward on file or message activity will contain a link that will bring you immediately, when you click on the link, to the login (or resumes your session), then on to the item the notification was about.
i.e.: if you received a notification about a Message in your Workspace, DO NOT reply to that email (it wont be received). Instead, click on the link in that email to be brought to the secure Message system in the Portal to SECURELY reply there.
Or you can visit the owner's website (if applicable) or visit the owner's custom Portal URL to login to their Portal/your Workspace, and then navigate to the item you were notified about.

see also: https://help.dollaradaysites.net/knowledgebase.php?article=150