Summarize the following:
To create the slap brush texture you will need a paint roller and some texture brushes. If you plan on doing the ceiling as well, get a pole for your roller and brushes. You can find these at any hardware store. The texture brushes may be marketed as "crow's foot" brushes. Load your paint roller up with drywall compound and start rolling in vertical lines. When you finish rolling one direction, repeat the process in the opposite direction. You aren't adding more mud to the wall, rather your goal is to make an even surface.  After you've rolled in the opposite direction, make another pass with horizontal lines. Crossing directions helps to smooth out any lines from rolling.  Work with a 1/2 inch to 3/4 inch (1.25 to 2 cm) roller for best results.  As you pull the roller out, give it a slight shake to remove any excess mud. As you apply the compound, you want to avoid dripping compound down your walls.  If you have a hopper gun, you can choose to spray the compound on the wall rather than roll it. Either way, try to keep the layer even. Apply a generous amount of drywall compound to your texture brush. Hold the brush perpendicular to the wall and "stamp" the brush onto the wall. Pull the brush off the wall and keep stamping the wall, working in sections. To vary the pattern, make half turns with the brush with every stamp. Don't turn the brush while it is touching the wall, as that will make a smoother, swirled pattern. The goal of the slap brush technique is a rough texture. Dip a taping knife into some of the drywall compound and run it across the edges to smooth out any angles. Wipe the corners from the inside out. Put the edge of the brush into the corner and pull away from the angle. Let the drywall compound dry completely before adding another coat of primer. Once the primer has dried, paint the room as normal.

Summary:
Gather your supplies. Roll out your compound. Load up your texture brush. Wipe the angles. Finish the texture.