After you've made an enquiry, you're satisfied with the details and you're ready to proceed, you can make a formal proposal. Go back to the enquiry and you'll see a button Make proposal. Click it, and fill out the known details: dates, who is travelling, which home you're exchanging if you have more than one. Click Send and the proposal will be sent to the other member. The member will then need to accept the exchange and, when you're ready, finalise it to lock in the details.