need help reading a pattern

[crowklc]

Hi I am a beginner at knitting. I am working on a slipper kit. In the instructions for shaping the heel at the end it says: Fasten off--not bind off but fasten off. I am not sure what this means or how to do it. The next instruction tells me to Make Gusset. With right side facing, pick up and knit 9 heel flap stitches along right side of heel. With 2nd needle knit across 10 heel sts from instep. With 3rd needle pick up and knit 9 sts along next side of heel, K 16 sts from st holder. Use marker to beg of rnd. 44 sts.
I have watched videos and looked at instructions but I haven't found anywhere to fasten off.
Can someone tell me what I should do? I have thought about incorporating one of the other patterns but am afraid I'll get to a point where I am in way over my head.
thanks
kc