Make your sprite jump when you clap is a video in a series of video tutorials under the Help tab on the Scratch main head bar. It describes how to use the loudness value to make a sprite jump. The video is 2 minutes and 6 seconds long.
[0:00] In this video, we will make our sprite jump every time we clap our hands. clap, clap.
[0:08] To make this work, you will need a microphone.
[0:18] To do this, I will grab the set y block.
[0:38] ...and grab the loudness block.
[0:45] Loudness uses the microphone in your computer to detect the volume of the sounds you are making. I will set loudness to the y value to our cat.
when gf clicked forever set y to (loudness) end
[1:05] When you click on the green flag, Scratch may request your permission to access you computer's microphone. Click allow.
[1:15] Now when you clap your hands, the cat will jump.
[1:21] To make these jumps a bit more pronounced, I will click the Operators link in the palette...
[1:32] ...and grab the multiplication block.
[1:40] I will multiply loudness with, let's say, four. You can play around with any numbers here.
when gf clicked forever set y to ((loudness) * (4)) end
[1:52] Now when you make a sound, the cat will jump higher.
[2:01] Finally, can you make the cat move in a horizontal direction when you clap?