In invoicely, each of your clients can be assigned individual contacts, which are most often used to deliver invoices or estimates to multiple representatives of client organizations.
In order to add a contact for one of your clients, please navigate to Clients, choose a client and click the righthand "Edit" button. On the following page, choose "Manage Contacts" from the top right Actions menu.
You will then be redirected to a list of all available contacts for this client. In order to add a new one, click the top right "New Contact" button, enter all required details and don't forget hitting "Save".