I have a Digitech RP 50 series pedal and wanna get it sound like some specific groups'(Pantera,Metallica, Red Hot Chili Peppers); or like some specific songs' effects(Nothing Else Matterr etc...) Can anyone help me please?
Exit light
Enter night
Take my hand
We'r off to never never land..

METALLICA[Lord of the Acoustic Metal]
Dude. Just....mess with it. lol Theres nothing more you can do but just tweak it to what sounds good to you. Trial and error.
Yeh, you just have to spend time figuring out what sounds like what.
But heres a tip...
Rectifier, Fuzz and Marshall/British Stack amp models are the heaviest amp models
High Gain Tube and I think the Hot Rod are pretty good OD for rock and stuff
Tweed, Boutique and the amp model starting with a U, are good cleans with tiny bits of gain (if you get what I mean)

But yeh, fiddle with the Gain of different amps, then fiddle with the EQ (trust me, the EQ changes everything)

If you're looking for effects, same thing, fiddle around with it.
The most common I'm guessing would be Chorus, Flange or Phaser for solos and stuff. (or Harmonizers)