For the L, cut approx 1 1/2" of l-fabric and attach to a wide bit of background. Then whack off the extra.
Attach perpendicularly to some l-fabric, and again trim. There's the L. In this photo, I'm also showing the beginning of my U (on the left), cuz yes, it is an L too before the final bit is added. For the U I started with a skinny rectangle of b-fabric and added it to my widest l-fabric. I point this out to show that even I explain construction one way, there are always other ways to do it. The only important thing is that it looks like the letter you want.