Cover all areas that you do not want textured with plastic tarps, held in place with low-tack painter's tape.
Mix a batch of drywall compound with water, following the instructions on the package. Add extra water to thin the mix until it has the consistency of pancake batter.
Connect a drywall spray gun to a compressor via an air hose.
Set the compressor's pressure to 30 psi.
Fill the spray gun's hopper with the drywall compound that you have thinned.
Set the gun's size dial, which determines the size of the particles that are sprayed and is located on the front of the gun. Select a smaller size if you want finer particles and a larger one for larger particles.
Spray drywall compound onto the wall, holding the gun roughly 2 to 3 feet away and sweeping it back and forth in smooth, overlapping motions.
Let the texture dry overnight.