|This technique is about sewing triangles of fabric together without having to cut triangles, and more importantly, to not deal with the stretchy bias raw edge[s] that all triangles have. You just cut squares of fabric on the straight grain of the fabric.
Now before you stop reading, this is not just for quilts. 'Half square triangles' [a square cut in half diagonally...one bias edge] and 'quarter square triangles' [a square cut diagonally both ways...two bias edges] can embellish and give extra interest to many things:
A fabric purse or totebag can have several of these units sewn together to form a strip of decoration along the top or bottom of the bag.
A pillow cover can have borders, or be made entirely of these units.
I've even covered a big heavy button with a quarter square unit, to use as a weight on a purse flap.
A decorative hemline on a little girl's dress. Or added to a top, with coordinating pants...the triangle units made using both fabrics.
Add as appliques in contrasting fabrics...a great way to use leftover fabric scraps.
The possible uses are endless.
The web link above has instructions and images explaining this technique. Note that these instructions do not include seam allowances. Normally this type of triangle unit is sewn to another unit with a 1/4" seam, so add 1/2" to your fabric square size to allow for this, when determining the size you want.
Tip...press each unit as sewn, then press open on the RS of the fabric, pressing the seam allowances to the darker fabric side. Do this gently, as you can still stretch the bias with vigorous steam ironing.