Particles are tiny little dots that move with real world physics. You can take these dots and make them into other things, like smoke or shell casings then have then react like real objects. But far particles are one of the most things to play with!
There are several particle generators on the market. 2D generators like Effects Lab produce particles as you guessed in a 2D plane. Another 2D generator, Particle Illusion has amazing features like a simple wind and boundires to control particles in amazing ways.
Apple's motion and Trap Code's partuclar for After Effects work in 3D space so you can get amazing prepective with your particles. I used Particular as a light emmitter to eject particles from a single point, it works like a champ adding real word effects such as gravity, random spin from air drag.
I created the shell casings using Trapcode's Particular particle generator. Particular is a 3D particle generator with real world effects such as gravity and velocity, this way i could match the angle of the gun and have shells "fly" out of the breach in any imaginable direction. once the effect was created i exported the file for shake. This is the hardest to learn (watch some tutorials at Video Copilot, he uses them Alot!), but it has the greatest payoff.
My second particle generator is Wondertouch's Particle Illusion 3. This program has over 1000 pre-made effects including dirt hits, explosions and fire. Every particle can be altered in look and physics. Wonder touch puts out a new set of particles each month, the amount of prepackaged effects is staggering, the only draw back is it is 2D (they are working on a 3D version).
I love apple but I have to say i really don’t like motion, it crashes a lot. BUT if you already own the program I highly suggest getting to know it. One word of advise, save and save often.
EffectsLab (that makes muzzle flashes and “light swords”) also comes with a particle generator. While this is probably the weakest generator of the bunch, the package (EffectLab) is a great bundle for someone who wants a program that can do a lot of different effects.
There is also a particle generator for Combustion from Auto Desk, and I’m sure I’m missing a few more.