So I have played the piano for half a year now and I have a question about the sustain pedal. I have seen in a lot of piano videos that the sustain pedal only sustain the notes the you played when you pressed the pedal. Do I say something wrong and if it really does play only the notes that you pressed is it only on an acoustic piano because on my keyboard it sustains all notes that I was playing when I pressed the pedal and the notes that I play if the pedal is still pressed.
You're thinking about the sostenuto pedal. On good, expensive pianos, there are three pedals. The middle pedal on some pianos is a practice pedal, which moves a curtain between the hammers and the strings. The sostenuto pedal is different. The mechanism is designed to hold the dampers off only the strings played while the pedal is down. Like a very specific damper pedal (the right hand one).
The damper or sustain pedal moves all of the dampers away from the strings, so others that are not even played will vibrate in sympathy, so making a richer, louder sound. hence 'loud' pedal.
A lot of keyboards and electronic pianos have a socket where a footswitch or pedal can be connected, which then works just like the sostenuto pedal.