I highly recommend the book "Origami Tessellations" by Eric Gjerde if you are interested in tessellations: http://www.happyfolding.com/book-gjerde-origami_tessellations
This video demonstrates how to fold a rhombus twist. It is a technique that is often used in origami tessellations.
The rhombus twist works on a triangle grid. The video also explains the difference between a twist that rotates clockwise or counterclockwise. If you fill the whole paper with rhombus twists, then you will receive the tessellation "Rhombus Weave" designed by Eric Gjerde. See a picture of a "Rhombus Weave" I folded here: http://www.happyfolding.com/gallery-gjerde-rhombus_weave