Pitch effects add new notes to the one you play, or move your note somewhere else entirely. They range from subtle thickening to sounds that barely resemble a guitar.
Octave up and down
An octaver adds a note one octave below, one octave above, or both, mixed with your dry signal. An octave down fattens single-note riffs and can stand in for a bass line when there's no bassist. An octave up adds a bright, ringing, almost organ-like layer. Start with the dry signal at full and blend the octave in until it supports the note rather than replacing it.
Octave fuzz
An octave fuzz is a fuzz circuit that also generates a rough octave up. It's the sound widely associated with Hendrix and the Octavia. The octave usually comes through best on the neck pickup, with the tone knob rolled back, and played up around the 12th fret. Chords turn into a glorious mess, so save it for single-note lines.
Harmonizers
A harmonizer adds a second note at a chosen interval, often a third or fifth. "Intelligent" harmonizers ask you for a key and scale so the harmony stays in key, switching between major and minor thirds as you move. Great for instant twin-guitar lines.
Whammy-style pedals
A pitch shifter with an expression pedal lets you sweep your note up or down with your foot, from tiny bends to two-octave dives and screams. The DigiTech Whammy made this famous, so people call the whole family "whammy pedals". Try a slow sweep up an octave on a held note.
Drop-tuning pedals
These shift your whole guitar down a set amount, say a half step or a whole step, without touching the tuning pegs. Handy when one song in your set is in a lower tuning: one click and you're there. Expect a slightly processed sound compared with really retuning.
Polyphonic vs monophonic
Monophonic pedals can only track one note at a time. Play a chord and they glitch, warble or pick one note. Many classic analog octave pedals work this way. Polyphonic pedals can track chords cleanly, which you need for drop-tuning and most whammy tricks on full chords.
Whatever the type, play cleanly and mute the strings you are not using: stray ringing notes confuse the tracking.