A MIDI keyboard like this just tells your software which notes you pressed, how hard, and when you released them. What happens then is up to the software.
In GarageBand, you can select a Software Instrument for a track. Most, such as the pianos, organs etc. will simply produce all the notes you pressed, so to play a chord you play all the notes in the chord. But some of them - typically synth pads - will play a chord from a single keypress. Some play an arpeggiated chord. Some will play a repeating pattern. They're usually named descriptively.
You can easily explore the different instruments without an external keyboard. In GarageBand, open the Window menu - Musical Typing, which maps your Mac keyboard onto a piano-like arrangement.