The double points are a pain in the ass on the smaller sizes. I'm doing better with a set of size 4s....or is it 4mm. Meh.
Regardless, I'm using worsted weight merino following that pattern on Socks 101 and coming out okay, but starting was an absolute nightmare.
Jargon translation, DPN = double pointed needles. Circs (circular needles) are two needles joined in the middle by some fishing line or nylon.
Usually you transfer yarn from one needle to another in traditional knitting, but with circular needles you just join the two ends of whatever you're working on, go round and round and slide it on the line.
Worsted weight is a yarn thickness that's erm, maybe a third the thickness of thin clothesline. Sports weight is thinner yarn, so your socks don't come out something like .5" thick.
A heel flap is a heel flap, and an instep is an instep.