For your first go at stencilling you'll need to gather a few things..
A stencil - start with a small stencil you can practice with.
Paint - choose a thick water based paint like an artists acrylic paint or thick emulsion.
Stencil brush - flat ended brushes designed for painting stencils.
Tape or spray mount - low tack tape or repositionable spray adhesive.
Paper plate, kitchen roll. Large pieces or scrap paper or card.
Start by putting a small amount of paint onto a paper plate, have a separate brush for each colour you're using.
Lay the stencil in place on paper or card, secure with tape or use spray mount adhesive.
If you're using spray adhesive follow the manufacturers instructions on the can.Make sure you only spray the reverse side of the stencil, don't use too much, protect the surrounding surfaces and wait for the glue to dry on the stencil. Aerosol glues are best applied in an open space or outside, we use a large cardboard box, place the stencil inside and spray it.
Take a very small amount of paint onto the flat end of the stencil brush, dab the brush onto a clean part of the paper plate to evenly distribute the paint onto the bristles. Next, dab the brush onto a paper towel to remove any excess paint. The main thing here is to have the bare minimum of paint on the brush.
Keeping the brush at a 90 degree angle to the stencil gently tap or dab the brush on the stencil, once you get a feel for the amount of paint that's on the brush you can start to tap harder. Keep tapping in a woodpecker motion, pressing more and more firmly until it's impossible to get any more paint from the brush. Reload, distribute and remove excess paint and start tapping again! Pay attention to the edges of each cut out shape to retain definition to the design.
Once you're happy that all areas are painted you can peel away the stencil to reveal your work.
Clean brushes and stencils with warm soapy water and a soft nail brush.