You take the gondola to the top station then ski down to the start of it. The first bit is a bit hairy scary though. Went there as a first timer in March but managed it OK.
You also have to cross the paths of other drag lifts.
Good Luck!
There are piste maps and lift maps on this site.
http://www.bulgariaski.com/cmim.php?pic=fmimages/borovetsmap_sm.jpg