The slap technique is most commonly used by bass players. But slapping can also be done on a guitar, typically electric. There are three basic elements to slapping. One is to slap with the thumb of your right hand over the pickups. The second is to slap with multiple fingers of the left hand onto the strings over the fretboard. The third element is to pluck notes using available fingers on the right hand. Using these three elements to make a slap sound, you can combine them in any order to make whatever rhythms you want.
If you alternate fretted notes with open strings you can create a cascading sound of awesomeness. The video below describes how you can take a scale and substitute as many fretted notes as you want with open strings (E, A, D, G, B, E). The beginning of the lick in the video starts off by descending the G Mixolydian scale (G, A, B, C, D, E, F) from G: G (fretted), F (fretted), E (open), D (fretted), C (fretted), B (open), A (fretted), G (fretted). The video below shows the rest of the lick. This second video demonstrates descending and ascending scales while using open strings!