When you receive an incoming call, the following screen pops up:
You will see the name of the contact who is calling and other information. You have the possibility to select from the dropdown list the contact that is really on the call with you. DIAL|IT gives you a selection of contacts that match the caller, depending on the configuration of your addon.
Use the icon to add the caller's phone number to an existing contact. You create a new contact by clicking on the icon. When you go to the icon, you go to the contact that DIAL|IT suggests at the top.