Weight is the thickness of the yarn
To chain is to wrap your crocheting needle around the yarn and pull a loop through the loop on your crocheting needle.
Beginning / Beg
Refers to the beginning of indicated round/row, or foundation chain. Or indicates a beginning stitch or sequence of stitches.
Rounds / Rnds
Crochet is basically worked in rounds or rows. To round is to start the next row.
Turning chain / Tch
The chain stitch(es) specified in pattern instructions for turning work back in the opposite direction for beginning the next row.
Single Stitch / SC
Point your crochet hook through the next stitch, through both loops, pull a loop through the stitch but not the loop on your hook, then pull loop through both on your hook