Hi and welcome to KH. Congratulations on learning to knit! Increasing accidentally is a common problem and there are different ways it can happen. If you're changing between knits and purls it's easy to have the yarn go over the needle instead of between the needles and then it will get knitted on the next row and you've picked up an extra stitch. If you're not paying careful attention at the end of the row when you turn you can pick up an extra stitch there too either with a yarn over the needle or by knitting both legs of the last stitch. Count each row and try to see where you're getting new stitches added. You might want to read through FAQ...Mysterious extra stitches? Look Here! We've all been there. A little practice and it will happen less often.
Happiness is catching that dropped stitch while it's still fixable..
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Few questions first...Are you following a pattern and if so which one? Are you doing garter stitch (knit every row)? Are you a new knitter?
It's common for new knitters to add extra stitches. The most common cause is an increase called a yarn over (YO) which is created by having the working yarn in the front of the work instead of the back. If you are changing between knits and purls make sure the yarn is moved to the back when you're reading to do a knit stitch.
When asking questions ALWAYS post the name and a link for the pattern if you have it.
Sometimes it halps to pull the working yarn down and to the right before knitting the first stitch on a row. Then you can see that there is one stitch at the end of the left needle, not two. If you pull the working yarn up and over the needle, it'll look like two stitches.
You might try putting markers (a circle on contrasting yarn works) one stitch in from the ends. Then you'll easily be able to see if the extra stitches are coming from that pesky first stitch. Just slip the marker from one needle to the other, don't knit it.