ok well… i am VERY new at knitting… just learend a few days ago. and i had some cheap normal knitting yarn. and a kept gaining stiches like CRAZY… so i started over and kept gaining and gaining stiches. so i got to about 10 rows ( knitting a scarf) and decided to switch to fuzzie yarn… the cheap dollar store stuff aswell. it was going good the two yarns together but then i decided to star over. so this time i STARTED with the fuzzy yarn. and havent gained any stiches and im on the 3rd row… so was it the yarn or …i have no clue but i hope i dont start gaining stiches on this one…:mrgreen:
Extra stiches..(yarn)
Are you doing just a knit stitch, or knits and purls? Most likely, you are either knitting with the yarn in front, or purling with the yarn in back, either of which loops the yarn over the needle in between stitches and causes you to have extra stitches. When you do this on purpose it’s called a yarn over. 
It’s a common mistake for new knitters.
The other common mistake is in knitting every row, if the yarn is up over the top of the needle at the end, it pulls up the last st so it looks like there’s two stitches. Hold the yarn off to the side and you can see just the one st. There’s a sticky on extra sts here - http://knittinghelp.com/forum/showthread.php?t=32886