If pattern say "Yf, k3", Do I only have yf on first stitch or put yf on all 3 stitches?
Just do yf one time.
Here are two "yf" examples to show the differences.
"yf, k3" Means you only have to do "yf" once and then knit 3 sts.
"yf, k1 3 times" means do yf, k1, yf, k1, yf, k1.