Watch the Percussive Slap Technique online guitar lesson by Dmitry Lisenko from Percussive Acoustic Bass (Foundry)
Slap bass is a very popular style of playing bass, and there are a lot of great schools and lessons available where you can learn and master the technique. In short, thumb hits are called "slaps", index or middle finger plucks are called "pops". There are 2 main techniques - upper or lower slap, and it's usually dependent on how low your bass is positioned. I'll show you only how to use slap & pop in relation to percussive style bass. I highly suggest that you learn this technique additionally.