If you want to add a contact, you must first ensure that they have a company. (PD doesn't currently support individual contacts - if there is sufficient demand we may address this).
If the company already exists, you simply need to find that company record and add the new person via the "Other Options" drop down.
Note that as you type in their name, the initials box and email box will be populated for you - the email will only be populated if you have previously set up the company's email domain name and set the email template format, as discussed here.