New Customer
Login to dashboard click customers and on the left side there is a button New Customer.

Step 1: Click on new customer and fill all the details related to customer. Click on Save.

Step 2: After filling all the details , you can see all other options related to the customer like contact, notes, invoices, projects,etc.

You can also choose if you want to send the Welcome client email template which is configured in Settings Menu -> Email Templates in clients part.
Now your client can login in the clients area from the url www.yourdomain.com/clients/login
You can add new customers very quickly from the Quick Insert button on the top left dashboard menu.