A cymbal is a round metal percussion instrument. Crash, ride, and splash are common types, and they add width, shimmer, and strong punctuation to a song.
The basic idea
A crash suits emphasis such as the top of a section, a ride suits a steady pattern, and a splash suits short accents. How often you play them changes the impression.
Using it in performance and programming
Place a crash at the top of a chorus or a drop to emphasize the change. Keep them to the spots that need them so the high end does not build up too much.
How it differs from related terms
Cymbal is the general name for large metal percussion, while a hi-hat is a dedicated pair of cymbals used together.
Rather than playing them constantly, using them at peaks and section breaks makes their effect clear.
