The half square triangle unit is probably the most commonly used patch in a quilt block -- well it is second only to the square. It is made simply with two triangles, filling up half the square each -- hence the name. Take a quick look through this website, or in any quilting magazine, and you will start to notice that this half square triangle, regardless of its size, is present in more quilts than not.
Back and Forth
Free Quilt Block Pattern
The Back and Forth quilt block belongs to the nine patch category, but it is an "uneven" nine patch block since the three rows of three patches each, are not all the same size.
This quilt block is an easy block to build your skill set.
These two quilts shown, each use four of the blocks, rotating each of those four blocks by 90 degrees, and then setting these larger blocks, side by side. If you look closely, you will notice that one of the quilts also uses sashing to separate the blocks. Also changing up the border fabric selection can make quite a difference.