Its quite common to get holes when you first start knitting namely from dropping stitches without relising. Try counting the amount of stitches at the end of each row until you manage to stop this. As for joining in new colour check out the video section on this site under tips are some explanations that really helped me. It easier than it sounds. Trust in yourself.
Resist the temptation, Resisit the temptation...oh well i tried!!!