There is a section within your Brief page called "Questions". Here, you can ask the client more details about the Brief before submitting a Quote, continue a conversation about a Brief, as well as be booked. You do not need to submit a Quote before asking a Question.
You can ask a Question by clicking on the link to the Brief, then by clicking on the grey button "Ask Question to Buyer" underneath the Brief description. The button looks like this:
You can also ask a Question by scrolling to the bottom of the page. The section looks like this:
Read more about Questions in our User Guide.
Note: Conversations between you and the client will only be seen between you and that client. Therefore, any discussions taking place in this section are private.