Here is a quick demonstration using custom stencils from Pre-cut Patterns.
This video will demonstrate how to prepare a stencil for etching.
First remove the backing sheet, exposing the adhesive side of the stencil.
Then position the stencil on the glass.
Remember the adhesive is position-able so you can move the placement of the stencil before you rub it down.
Once you have the stencil in position, press it firmly to the glass, working out bubbles or wrinkles all the way to the corners.
Remove the transfer sheet and the stencil is ready to weed.
Use a craft knife or another picking tool to pull out the areas of the stencil that you want to etch.
Then you can apply a masking tape around the edge of the stencil to protect the glass from the etching cream, or overspray from sandblasting.
Now the glass is ready to etch!