This article gives a brief introduction about how to do. You will use your thumb (to slap) and index or middle finger (to pop). A pop (sometimes plucking) when you slide your finger selected slightly below the string and pull it away from the button. This should make a nice twangy sound

1. Keep your hand perpendicular to the strings and your thumb at an angle of 50-60 degrees with the string slaps. You must have an arm angle. Think of a traditional scarecrow with rigid upper arms. This may hurt after a long period of play, but you will get used to.
2. Remember, it's all in the wrist. For a basic slap exercise, you can slap and pop an octave - an octave is 2 frets up and 2 strings up. Play an octave with the first and third fingers left.
3. First, the position of his right hand. You need your thumb parallel to the chain (let's use the E string first)
4. Now, using a hitchhiker or flopping fish action, slowly bring your thumb down and hit the string, the string when you hit the string try and hit on the lower half of it, the bottom of your thumbs should end up in the next string.
5. Continue practicing until it hits rather than action to achieve the ideal sound is a solid hit.
6. Now, try adding a touch of pop to technology. Popping is where you pull the string.
7. Whether your middle or index finger (which is becoming more comfortable) put your finger on the string that uses the G-string, pull your finger up until the string snap the fretboard.

Here is example video