Could someone explain what these means and how does it affect the pattern if I just knit 2 together?
Thanks
Look under view videos on this site. You’ll find “ktogtbl” under decreases…with a great video and what it looks like finished. Good Luck.
Knitting tbl causes the sts to twist (unlike k2tog). There’s a reason for the twist.
cam
Do you know how to knit one stitch through the back loop? It feels a little different than knitting, because you put the right hand (RH) needle into the stitch from right to left, [U]behind[/U] the left hand (LH) needle. After you have the needle inserted, you just yarn around and knit the stitch like a regular knit.
To knit 2 together through the back loop, you just do the same thing, but instead of running the RH needle into the first stitch right to left, behind the LH needle, you run it through both the first and second stitches. Then you yarn around the needle like normal and finish knitting the stitches together. You just made 2 stitches into one and twisted them so that the legs of the stitch form a little “X” at the base. Unless the stitches were on the LH needle backwards, then knitting them tbl would straighten them out, and the result would look like a regular K2tog. 
It is not any harder than a K2tog once you know where to insert your RH needle. The videos will be a big help if you can view them.
It usually affects the pattern quite a bit if you k2tog instead of k2tbl. The k2tog will cause the stitches to lean right; the k2tbl will make the stitches lean left. If you use the wrong decrease, your work will have a zigzag or maybe a twist that doesn’t belong!
Give the k2tbl a try and after a couple of times, you’ll be wondering why you were so worried! 