First you will need two charm squares to make a pair of half square triangles. Click on the above post on how to make a half square triangle.
Now pair each of the half square triangles with another charm square of your background color, placing right sides together. Your background charm square will be 1/2" larger than your half square triangle. That's ok. Just eyeball the half square triangle in the center of the 5" charm square. It will just give you a little bit extra wiggle room to square it up later. Draw a diagonal line from corner to corner, opposite the way the half square triangle is.
Sew 1/4" from the drawn line down each side. Cut apart on the drawn line. and press to the background triangle.
Once again I like to use the Quilt In A Day Fussy Cut Rulers to square the quarter square triangles up. This one happens to be 3 1/2". As you can see you have plenty of "square up room" and you could actually square this to a 4" square if your pattern calls for that size. I am using 3 1/2" as that size works well in my scrap busting system that Bonnie Hunter recommends.
You will have 4 quarter square triangles using this method.
With these basic block components you can put together or create many, many, many block combinations. Be creative... make a few of the block components and play around with the layouts. The other nice thing about all these block components is that they all can be squared up to the same size if necessary and play well together with lots of block combinations.