The length and thickness of these wires vary, and by changing the length and thickness of these wires, the pitch of the sound is changed. The length and thickness of these lines vary, but by changing the length and thickness of these lines, the pitch of the note is changed.
When you strike a piano key, a hammer connected to the key moves and strikes each piano wire to produce sound. In the piano, instead of plucking the strings with fingers or bridges, the strings are plucked with small hammers.
However, just plucking the strings with a small hammer does not produce a very loud sound. Therefore, a large box is placed over the strings and the air inside the box is shaken together to make the sound louder.
The mechanism for producing sound is the same for a grand piano and a vertical upright piano. The only difference is whether the strings are stretched horizontally or vertically.

Electronic pianos (electronic organs and electric organs) are completely different from pianos in that they create vibrations electrically and use these electrical vibrations to sound the speakers to produce sound.