How do I individually enter new members and fill out their profile?

When you want to add a new member, go to the Members page. Use the + in the upper right and choose Add a single member to open a new profile. 

A new member pane will appear, allowing you to add as much information as you like to the profile. 

Note: The profile must have either a cell or email to be saved. 

Regardless of the way you add members, all new members will immediately be sent email or text message notifications for all group activity.