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.
Free Quilt Block Pattern
This is a simple four patch block to make, using only squares and half square triangle patches.
The sample quilts illustrated use the block on point (with rotation of some of the blocks in the quilt) and blocks set side-by-side -- again with some of the blocks rotated. As you can see you can do lots of interesting variations with regard to placement of this quilt block to make your own precious heirloom.