Some artists love the textural feel both visually and physically on a canvas and are quite adept at adding color to a thick medium or impasto gel. Applying the paint can be done in various ways, palette knives are commonly used because of the viscosity. Often times people will pour the thickened paint on their chosen substrate and scrape the paint using combs, sponges, scrappers and then create raised designs, lines and swirls.
You can always add the medium unmixed to your canvas and paint over it after it’s dry. The thicker the medium, the longer it will take to dry but you will have a more detailed artwork.
You don’t need to buy expensive stencils but can rather make your own by using cardboard or plastic materials. Trace a found image or create one of your own by lightly drawing it, and then carefully cutting it out using a utility cutter. Lay your stencil onto the canvas and apply your mixed paint and gel medium with a palette knife.