Formal western classical music is composed of harmony, melody, and rhythm. Some musical forms eliminate one or more of these elements. In Indian classical music, there is no harmony---the melody rises out of a background drone "like a mountain raising above a prairie." In hip-hop music, melody and harmony are absent leaving only rhythm. When hearing someone whistle a song badly, melody might be the only component. Music is largely a cultural phenomena---we evaluate a musical piece based on what music we have heard before. For most Americans, if a piece is not in either the Major or Minor key, it sounds "foreign" or "wrong." For Indians, harmony causes music to sound "off" or "muddy."
"Tempo" is the Italian word for "time." Tempo is the regular, measured pulse of a piece of music. It should not be confused with rhythm which is how the notes in the music fit into the tempo. The tempo can be increased or decreased for effect by some performers---slowing the tempo makes music more dreamy, speeding up the tempo makes music more exciting. Classical composers suggest a tempo with a single Italian word or phrase above the staff at the beginning of a work. For example "Adante" means "at a walking pace" and "Lento Moderato" means "moderately slow."
Pitch is the vibrations per second of a single note. The standard pitch in western classical music is A440. It is the note A above middle C which is 440 vibrations per second. The oboe gives this note before the beginning of concerts for the rest of the instruments to tune to because the oboe is hard to tune and has a piercing note that is easy to hear among the other instruments. When some instruments are played alone they are tuned using "relative pitch." For example a guitar that is being played without other instruments is tuned so that each string has a pitch that is correct in relation to the other strings, although the A above middle C is probably not exactly equal to 440 vibrations per second.