Knitting verbage and decreasing rows

[detailoring]

I'm BRAND NEW to knitting, only been doing so for about a week-and-a-half. I've worked it out that I can make a halfway decent scarf. I'm not too great on changing colors yet--kinda figured that one out on my own--but it's a start. ((I taught myself to knit using the videos from this site!!!!))

I'd like to make a couple of very simple things.
http://www.knittingatknoon.com/mittenpatt.html
http://www.knittinghelp.com/knitting...opic.php?t=123

They're going to be for my son who is closing in on 1 year (roughly in 18mos clothes), but I'm not sure how to do so. I don't understand a lot of the terms in them:
"worsted weight yarn"
"kitchener stitch"
"mattress seam"
"Stockinette stitch"
"k2tog"
"kfb"

Also, I don't know what it means by decreasing the rows by "x" stitches. I may just end up hunting down somebody in the area--walking up to a random stranger, "Hi, do you knit?", haha--and asking for help. But I figured I'd ask here first.