When I started knitting, I did everything really tightly (still have a tendency to do that). But I can't say I had that problem. Did you view the videos on this website? http://www.knittinghelp.com/videos/purl-stitch
What you are doing when knitting or purling, really, is putting the needle through a loop, grabbing a loop of working yarn, then pulling it back through where you just went in.