Yarn forward adds a stitch and skpo will decrease a stitch. Check and see how many of each are in your pattern row. It may be that you have a net increase on one row and then decrease on another later row. You might also check the Glossary for both terms just to make sure you're doing them correctly.
Can you give us a link to the pattern or a pattern name?
Look at the decreases page - skpo is known as sl1, k1, psso (pass the slip stitch over [the knit stitch]). Yfd is a yo and is just wrapping the yarn around the needle; doing the next stitch in the pattern will anchor it.