Krystyna,
I also have this serger and love it. I found preaty good video on how to thread it on youtube - filmed by young woman, and threading is a snap now, there is also another video on how to figure out the tension.
http://www.youtube.com/watch?v=5ohtf7H_gyc how to thread
http://www.youtube.com/watch?v=NTdjgIKIBr0 how to figure out tension problems
I found them to be very informative, and was able to thread my serger right way first time
