on the piano"1-3-5"A chord represents a basic third chord, usually consisting of a root note (1), a third note (3), and a fifth note (5). These numbers refer to positions in the scale based on the specified notes. In C major, for example, the root note (1) is a C note, the third note (3) is an E note, and the fifth note (5) is a G note. "1-3-5"Chords are chords played with the left hand, in C major"1-3-5"Chords, place the thumb of the left hand on the C note, the middle finger on the E note, and the little finger on the G note. When playing, press all three notes at the same time to play"c"of"1-3-5"Chord. 
This rule can be applied to chords of other scales. For example, for D major"1-3-5"Chords, place the thumb of the left hand on the D note, the middle finger on the F note, and the little finger on the A note. During this process, we need to note that the position of different notes can be different, so the position of the fingers needs to be constantly adjusted to accommodate different chords. 
In order to become more familiar with the chords, it is recommended that you practice Xi them over time, gradually increasing the speed and precision of your fingers. Only through continuous practice can we master the piano playing skills and better interpret different Xi works. 