I don't have ipad's GarageBand, so I'm not sure what you'r looking for - do you mean a hand clapping effect?
That you get in GB with the Software Instrument "Sound Effects -> Applaus and Laughter"
To see which sound is produced by the different notes show the "Musical Typing Window" with Shift-cmd-K and select the oktave c2.
The keys labelled "A","D","F", and "G" produce clapping sounds. If you want a different clap-sound, record your own handclap and drag the loop to an empty key of the "Musical Typing Window". Then you can play it from the Sound Effects Instrument in your own Rhythm.