You don't even need to leave this site, Knitting Help, for videos. There are a number of videos linked to this
Watch whichever cast-on you used to see whether you did it correctly, then watch the knit-stitch and purl-stitch videos in either English/throw style or Continental/pick style (whichever you're using).
If you still haven't diagnosed where the long "string" is coming from, take a look at the "Small Project" video.
All of these are linked to the page I gave in my first paragraph--and there are many more videos, too! All well shot and clear.
P.S. I only learned to knit in May 2011, so I'm a fairly new knitter, too.