Particle routines are used in different scripts. There are some defaults included, but it is assumed you will wish to customize these to fit your own preference.

It is fairly simple to create a particle routine using a particle generator HUD or other particle generator device, most will spit out the complete code.
If you have another script with a particle routine that you like, you can copy the particle routine and paste it into place in the KCP script where a particle routine is triggered.

Particle routines start with this code: llParticleSystem([ and end with the closing pair or brackets: ]).

Simply by changing the numeric values and texture uuid's you can customize the routine.

Read more about particles here.