First you need to pass a panel interview where you present the paper chosen by the committee and discuss it with them and then they ask you about your previous research. If you are successful you have the opportunity to go on and talk with PIs to find a match. The PIs present their research on a poster-based scheme the first day (before the panel interview) and you can approach them and talk about their research, then you turn in a list with their names and if you were successful at the panel interview you have the chance to talk with them in a more informal way.