When a member signs up for a Free Membership Level, they receive an email to confirm that they used a real and active email address. In this email is a link to confirm their email address and make their profile live. If they have not done this yet, then they will appear as "Not Active" in the Admin area of your site.
When members are "Not Active", they will not appear on your live site, so it is important to make sure that all members who sign up for an account activate their profile.
You can resend the confirmation email to them by clicking on the "Unverified Email" link next to their profile information:
This will pop up a window with a pre-formatted email template that contains the link they need to click on to confirm their email address and make their profile "Active"
If you would like to make their profile "Active" manually, click on "Edit" for this member, set the "Account Status" field to "Active", and then save the changes: