Just a note - this is a less-precise process than cutting geometry...
Select Import... from the File menu, and select your image file.
Click to place the image, and resize according to the desired output.
NOTE - if you're etching into acrylic (or other materials that will turn lighter when etched) you may want to invert the colors in the image.
Select Print... from the File menu, pick the appropriate laser, and click the Properties... button.
Set the Pen Mode to RAST for Black and None for everything else (the software will automatically convert any images to grayscale). Note - any Black geometry that is not part of the image will also be cut at the settings below, and any geometry other than black will not be cut.
Change the speed to 33% (the max raster speed), the PPI to 1000 and set the power to a value between 10 and 30 percent, depending upon how dark you want your etching (15 works well for MDF, 20 is good for acrylic, but it depends upon what you want). Don't forget to hit the Set button, then OK a couple times to send the job to the laser.
Then it's on to Cutting Your Part...