Once you have sent your event invitation to one or multiple artists, they have an opportunity to express interest in performing. When an artist indicates that they are 'interested' in your event you will receive an email to your sign-up account, and a notification on iOS if you use the Six8 app.
From this point you are able to chat with the artist through the event page by clicking on the chat icon:
Artists can send you a quote for your approval at any stage after they have expressed interest. It is best to have a chat with them to make sure they know the exact specifics of you event.