The majority of FR's flights depart and arrive at an attached wing of the main terminal, which requires you to walk to border control on arrival, and to your gate on departure .... estimated at an optimistic 12 minutes.

Some of their flights go from the satellites which are reached by a shuttle from the departure lounge, as do all of Easyjet's flights.

There is another wing attached to the terminal for domestic flights, which is accessed on foot.

The Stansted Airport website is the place to look for lounge facilities, as Aviatrix mentions, or you might like to telephone them for more precise information.