This 3D pattern is created by knitting the loop aslant in opposite directions.
With a fluffy, coarse green yarn this pattern works best, and the stitch stays perfectly upright. I also did the same pattern with a 100% Alpaca yarn. The use of this beautifully supple yarn makes the effect less spectacular, because the loops collapse.
I also made the pattern in 100% alpaca.
The choice of yarn is determined by its appearance but also the feel of the material: hard, soft, pliant or stiff. With the fluffy, stiff yarn the stitch remains nicely upright.
On a flat-bed knitting machine the yarn, by means of a yarn feeder, is inserted into the needles and passes a needle bar from left to right and back. A bar is a metal surface with needles.