A lead is a person you have contact details for but who has no account yet. Leads let you collect and follow up with interested visitors.
Leads and users live in the same list. A lead can be tagged and contacted, but cannot log in. A user has an account and can sign in.
You find both in Users and leads, then Users, on the Users & Leads screen. The Is user column tells them apart.
Forms
A form with an email or phone User component saves the person as a lead when it is submitted.
Newsletter element
Each new email entered in a Newsletter box is saved as a lead.
By hand
Click Add user or lead, choose Lead as the User type and fill in their contact information.
If the email or phone already belongs to someone, the answers are attached to that person instead of creating a second record.
When someone signs up with an email, username or phone number that matches a lead, the lead is upgraded to a user. Their existing details stay, empty details are filled in, and their tags and form history stay attached.
The same happens when they sign in with a social provider that confirms a matching email.
Leads are only useful if someone follows up. The Users & Leads screen has the tools for it.
Add tags to leads to group them, for example by the form they came from.
Select leads in the table and use Send as SysAdmin email or Send as SysAdmin mobile message to contact them.
Use a form's User data option to decide whether later submissions may update what you already know about them.