In your contacts you can have your main Billing contact and you can also have other contacts for the same organisation this can be done in the Web Portal and in the App. 


To add a new person to an existing Contact in the Web Portal, CRM > Contacts > Select the contact you would like to add the person to > Select "People" > Use the + > + Add New Contact.





To add a new person to an existing contact in the App > Contacts > Select the contact you would like to add the person to > Select "People" >  + at the bottom right of the page to add the New Contact.





This can also be done when creating a new job