Hiya gram, n welcome to the party!!
K,to knit into the back loop of a stitch. Usually when you are doing regular knitting you insert your needle under the front part of the v, going sort of left to right, when you are knitting into the back loop, you insert your needle under the back of the v going sorta right to left with the right needle. Knit the stitch and in this case you are twisting them so you would leave that old stitch on the left needle with the new stitch on the right needle, bring your right needle around to the front and knit the skipped stitch normally, then slip both old stitches off the needle and have new stitches on the right needle
, you've just made a twisted rib stitch.