In the account bar at the top, click on the "+Contact" button.
Once you click the +Contact button, you will be taken to a page where you can fill out the contact's information.
You can enter in the source of the lead, share it with a team member or co-marketing partner, add general notes, add groups and more. Click “Save” at the top when you are finished.
Contacts may also be imported to your account through a .csv spreadsheet file. Please read this article for more information.