I don't understand?

would someone please tell me how to yf, k1.
The pattern says k1,*k2tog,yf,k1,yf,sl1,k1,psso,k3 repeat from *

A yf is the same as a yo. Just bring your yarn to the front of your work between the needles as if you were going to purl. When you work the next stitch you’ll get an eyelet and an increase.