There's some videos at knitting help that show how to fix a few mistakes - http://www.knittinghelp.com/videos/knitting-tips
- and on other pages there that show casting off, increases and decreases and many other techniques on the Glossary page.
To keep an edge from curling you need to use a garter or seed stitch as a border; knit 5 or 6 sts in it at the beg and ends of a stockinette stitch scarf. If your whole scarf is garter or ribbing, you won't need to do this though. Slipping the first stitch only keeps that edge stitch from curling under, it doesn't prevent the entire edge from rolling.