Tapping is a general word for using the picking hand for hammering and/or pulling . i.e. legato..
You should try to classify them, so you can easily master each techninque individualy.
1- Pick Tapping .. I'm sure you all know it.. Like Metallica's "one" , or Satch's "surfing with the alien", basicaly for fast repeated stuff .
2- One finger tapping ... The most widely used , like Van Halen's.
3- Multi-finger Tapping ... Steve Vai , do I need to say more ?!
4- Two Handed Tapping ... A lot of bassists use this one...An easy guitar example is Satch's "midnight" .
Of course you can always incorporate some bends , slides , vibratos or do the sweep-tap trick for extended arp's...
You don't have to learn all of these at once, and of course they are not in any particular order, begin with what seems easier or more usefull to you... Set your goal , practice slowly & precisely.