they have a specific area where the groups sell stuff, the so called "Grand Market". all the groups have a space in the big tent mounted there. each one is free to make their regulations, regarding activities and cost. it will be available in the group's space, generally a board explaining all. groups that are a little organized will post the regulations in their official blog too, prior to the event.
different activities can be made just like everywhere, but most of it will take place in another specific area, the "Greeting Square". the festival will make available a time table containing the specific hour which group will be there. they happen during the shows, so expect to lose some performances if you go there wanting to meet some groups.
this was the way it happened last year, of course this year can be different. (probably not)