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
The Poppy quilt block is a simple five patch block (so named as it is constructed on a 5 x 5 grid) and an easy one to construct. It contains only simple shapes, the square and rectangle, and another of the very common patches in quilt making -- flying geese. The simple circle shape that is the centre of the poppy is appliqued on top of the block as a last step.
As you will note, by rotating the block in a variety of ways you can achieve different arrangements that appear as "borders" for the blocks. You could also choose not to include the outer pieces (shown here in green fabric) for a simple poppy all on its own.
The sample quilts illustrated give you some ideas of possible ways to create your own quilt.