It means "through back leg." When you look at a stitch on a knitting needle, imagine it is a cowboy sitting on a horse and the tip of the needle is the horse's nose. One leg is closer to you, and one is further away. For most knitters (in the U.S. and western Europe), it is the cowboy's right, or front leg that is leading, and the leg on the other side of the needle (back leg) is closer to the horse's tail than the front leg. It is important to notice whether your cowboy is sitting this way because it will effect the result of the tbl maneuver if he isn't. Usually (in the U.S. and Western Europe) you insert the needle into the front leg when knitting. This produces a normal stitch. If you insert the needle through the back loop, it will produce a twisted stitch. This is sometimes used for decoration, or for tightening an area that tends to be loose. Hold the needles nose-to-nose and insert the right needle into the stitch that way. That will put you through the back leg and produce the twisted stitch.
Through back loop
I think you mean tbl (L instead of 1), which is to knit through the back loop. (Regular knit stitch is through the front loop).
It means Knit Off.
On a knitting chart, it symbolizes "yarn over" also, in some books/instructions, "yarn forward".
I have never seen it without the l as in tbl but perhaps a typo? tbl = thru back loop which means to knit it thru the back loop
Usually in knitting instructions, the letter P stands for purl.
It means Tablespoon (not Teaspoon)
I have the instruction book!
There are many websites where one can find these instructions. One good place to go is the knitting section of the About website. Another few good websites would be YouTube, LearnToKnit, and TLC.
You can find instructions on how to make knitted hats online at websites such as Martha Stewart, BHG, and the About page dedicated to knitting. You can also find a variety of knitting patterns available on websites such as Pinterest.
yrn is the abbreviation for 'yarn' - the material you are knitting or crocheting with
Grameen is the name of a knitting factory in Dhaka, Bangladesh.
There are instructions for knit and also for crochet at the link listed below.