What is the easiest way to use this stuff? When I am working on a block and need to applique pieces I am not sure how to cut it. Any suggestions?

wonder under is paper backed or just webbing?

either way you can trace the piece onto the wonder under, cut it out place it where you want it, then put the piece of fabric on top of it, then use a teflon pressing sheet on top of that and press!

I trace my pattern on the paper side of Wonder Under and rough cut the shape and iron it to the wrong side of my fabric and then cut out the shape. If the fabric is bigger than the WU you don't have to worry about it getting all over.

I do as Scissor Queen explained, and I also leave it rough cut until I am ready to iron it on. Then I do the final cutting. This way the edges stay really nice :D:D:D

One thing to remember with wonder under or steam a seam is that you need to mirror some of the designs or they will be facing the opposite direction. On some things (like letters and numbers) it will really make a difference.

Same here.