Alright, m1 is an increase. basically, that's saying you knit in the first stitch on the needle, then the yarn between that and the next stitch, you pull it up onto your needle as it is a stitch, then knit into that, then you knit into the second stitch, which is now the third stitch. On this site here, it shows a M1 increase with a pretty good picture of it...
they call it a left increase, so look for that one (not far down really)
So, you'll knit one, then do the M1, K1 to the end... that would be K1, M1, K1, M1, K1... You should end with a K1.
It's the same anywhere it shows M1, K1... sometimes, patterns want you to K1, M1... that's just the same thing, only switched around. 21st is yellow... st means stitch or stitches. There's a lot of abbreviations in knitting patterns, which makes them nice and compact, instead of huge books for one thing. Most of the time you can really guess what it means and be right. Just about any pattern will use exactly the same abbreviations... for instance, they'll all use the abbreviation st for stitches. http://knitknitting.com/abbreviations.htm
lists a lot of them, at least, and probably all that you'll use for now. I do notice they use dp for double pointed needles... there will be some people who use dpn for that but it's mostly the same. () anything in those always means you repeat that and it'll show how many times afterwards. For instance, (M1, K1) to end of row means you repeat that to the end of the row. (K1, P3) 4x means you repeat that four times.