I believe when you do a yarn over it adds a stitch to your knitting.
A lot of patterns call for yo’s and in that row also tells you to knit together a stitch to keep from making the knitting bigger.
Hope that helps.
Beth♥
A dishcloth with similar instructions was my first knitting project! When you yarn over (YO) you add a stitch. So…you will be adding a stitch every row until you have 44 stitches on your needle. The pattern I did had me increase (which is what the YO is) until I reached a certain number of stitches, and then decrease every row until I was back to 2 stitches. The result was a dishcloth in the shape of a diamond.
I forgot to add that Amy’s videos are excellent for seeing how increases and decreases should be worked. If you have slow internet service – as I do – you can order her CD (which I love!) and have the videos for quick access. Along with the site videos, my other most valuable resource is the original Stitch N Bitch book. She has excellent explanations and instructions that I have referred to many times – especially about increasing and decreasing, and why you would use certain increases and decreases.