In the Contacts Tab you will see all the current contacts/users on your website. You can filter them by groups or add a new one manually from the Add Member button.
If you click on the member you will open their profile page.
For each Member, you can see their name, email and any contact properties you have collected within their profile.
You can manage all of these from the Settings -> Properties.
You can also reset their password, or delete the contact/member.
You can modify each contact/member by clicking on the Membership Tab under their name:
If they have subscriptions, you will see a Subscriptions Tab next to the Orders Tab