XC stands for Cross Country. Rider's go round and round a loop course. The number of laps you do depends on the category you want to enter (see Categories on the event promotor website).
Not sure but still want to have a go? Enter the Novice event; this is a shorter course but over a fixed time - you can do as many of these shorter laps as you like (or can). It'll be a load of fun.
The course is about 7.8km; there'll also be a shorter Novice course (approx 2km)
Check promotor website for more details closer to event date.