You can score or engrave your design, depending what it is. Most people reverse the image and score it on n the back of the acrylic.
If you’re engraving, you might want to remove the paper backing so your finer details will show. You might get some fogging on the acrylic part that way, but it cleans up pretty easily with toothpaste and a little rubbing.
If you need a design to start off with, there are a few posted over in #free-laser-designs. Here’s one I did: Neil Gaiman Quote (you might need to adjust the width to fit your base).