No notification email (be it a welcome email or an unsubscribe confirmation) will be sent to the user if you edit it from this page.
Cancel : When clicking on this button, you return to the users listing and any modification is cancelled.
Add subscription : This button is available when the editted user has been saved at least once. Clicking this button will open a box where you'll be able to select some lists to subscribe the current user.
Save : Saves the current user and stays on the edition page.
Save & exit : Saves the current user and returns to the users listing page.
Name: Name of the user.
Email: Email of the user.
Custom fields: If you created some custom fields, they will be displayed below the Email field
Active: This field shows you the status of the user. If you turn it off, the user won't receive messages from your website in the future.
Confirmed: If you require a confirmation, the user won't be confirmed until he clicks on the confirmation link received by e-mail. Nevertheless, if you do not require a confirmation, the user will stay as "not confirmed" but it won't impact the send process.
Creation date: Created date of the user.
Source : The source shows you from where the user has been created
Each user has a history saving how it has been created, how it subscribed to the lists and other information. You can use this if some bots succeeded in creating a user on your site for example, or if you need to prove that a user willingly subscribed to your lists.
When editing a user, you can subscribe or unsubscribe it from one or more lists by clicking the "Add subscription" button or the "Unsubscribe" link next to each list.