I started with 36 stitches and now I have 43 after 41 rows. How did this happen?
Sounds like you did accidental yarnovers, split a stitch, you didn't drop the one you knit into off the needle so making two, or you knit into the first st of the row twice. Here's a FAQ with some ideas and suggetstions.
That's VERY common with new knitters. Check the link Sue gave.