Scroll to the bottom of the Project overview and you can see any Contacts that have already been assigned;
You can add already created contacts or create a new contact by clicking 'Add Contacts' in the top right:
You can search your already created contacts, or add a new one - newly created contacts will be saved in your Contacts app.
In Contact creation, you can type what sort of contact it is.
For more information on a Contact, select the eye button to open it in the Contacts app.