how to find proper chords for a classical piece? just tell me the way to do this and things that i should know

you would have to first identify the tonality, then use tonic, subdominant, and dominant chords in that particular tonality (I, IV, V)

Match the chord tones with the melody

Explanation:

example in the key of "C"

I would be the C chord would sound best with melody notes which include the C chord (C, E, G)

IV would be F chord (F, A, C)

V would be G chord (G, B, D)

I, IV, and V are different based on the tonality

The I is the tonic chord and matches the key of the piece.