If you scroll down this page, there are videos about correcting mistakes. That should help with your first question.
As for holes, there are different reasons for them, and they are very common when you first start. Just watch each stitch--sometimes the stitch below the one on the needle gets picked up, sometimes the yarn is on the wrong side of your work. As you get better at knitting, you get a good feel for each stitch and eventually don't have to watch each one like a hawk. Just knit a lot and purl a lot--practice is really the key.