Particle system in unity3d

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Particle Systems

Particles are essentially 2D images rendered in 3D space. They are primarily used for effects such as smoke, fire, water droplets, or leaves.You can use a Particle Emitter and Renderer together if you want static particles. Particle Systems in Unity are used to make clouds of smoke, steam, fire and other atmospheric effects. Particle Systems work by using one or two Textures & drawing them many times, creating a chaotic effect.
A Particle System is made up of three separate Components :
1)  Particle Emitter
2)  Particle Animator
3)  Particle Renderer

Ellipsoid Particle Emitter

The Ellipsoid Particle Emitter spawns particles inside a sphere. Use the Ellipsoid property below to scale & stretch the sphere.

The Ellipsoid Particle Emitter Inspector

Properties

Emit	If enabled, the emitter will emit particles.
Min Size	The minimum size each particle can be at the time when it is spawned.
Max Size	The maximum size each particle can be at the time when it is spawned.
Min Energy	The minimum lifetime of each particle, measured in seconds.
Max Energy	The maximum lifetime of each particle, measured in seconds.
Min Emission	The minimum number of particles that will be spawned every second.
Max Emission	The maximum number of particles that will be spawned every second.
World Velocity	The starting speed of particles in world space, along X, Y, and Z.
Local Velocity	The starting speed of particles along X, Y, and Z, measured in the object's orientation.
Rnd Velocity	A random speed along X, Y, and Z that is added to the velocity.
Emitter Velocity Scale	The amount of the emitter's speed that the particles inherit.
Tangent Velocity	The starting speed of particles along X, Y, and Z, across the Emitter's surface.
Simulate In World Space	If enabled, the particles don't move when the emitter moves. If false, when you move the emitter, the particles follow it around.
One Shot	If enabled, the particle numbers specified by min & max emission is spawned all at once. If disabled, the particles are generated in a long stream.
Ellipsoid	Scale of the sphere along X, Y, and Z that the particles are spawned inside.
MinEmitterRange	Determines an empty area in the center of the sphere - use this to make particles appear on the edge of the sphere.

How To Add It in your Scene : 
Steps : 
1) add a Particle System
2) Components->Particles->Particle System.

Particle Animator

Particle Animators move your particles over time, you use them to apply wind, drag & color cycling to your particle systems.

The Particle Animator Inspector

Properties

Does Animate Color	If enabled, particles cycle their color over their lifetime.
Color Animation	The 5 colors particles go through. All particles cycle over this - if some have a shorter life span than others, they will animate faster.
World Rotation Axis	An optional world-space axis the particles rotate around. Use this to make advanced spell effects or give caustic bubbles some life.
Local Rotation Axis	An optional local-space axis the particles rotate around. Use this to make advanced spell effects or give caustic bubbles some life.
Size Grow	Use this to make particles grow in size over their lifetime. As randomized forces will spread your particles out, it is often nice to make them grow in size so they don't fall apart. Use this to make smoke rise upwards, to simulate wind, etc.
Rnd Force	A random force added to particles every frame. Use this to make smoke become more alive.
Force	The force being applied every frame to the particles, measure relative to the world.
Damping	How much particles are slowed every frame. A value of 1 gives no damping, while less makes them slow down.
Autodestruct	If enabled, the GameObject attached to the Particle Animator will be destroyed when all particles disappear.

Particle Renderer

The Particle Renderer renders the Particle System on screen.

The Particle Renderer Inspector

Properties

Materials	Reference to a list of Materials that will be displayed in the position of each individual particle.
Camera Velocity Scale	The amount of stretching that is applied to the Particles based on Camera movement.
Stretch Particles	Determines how the particles are rendered.
Billboard	The particles are rendered as if facing the camera.
Stretched	The particles are facing the direction they are moving.
SortedBillboard	The particles are sorted by depth. Use this when using a blending material.
VerticalBillboard	All particles are aligned flat along the X/Z axes.
HorizontalBillboard	All particles are aligned flat along the X/Y axes.
Length Scale	If Stretch Particles is set to Stretched, this value determines how long the particles are in their direction of motion.
Velocity Scale	If Stretch Particles is set to Stretched, this value determines the rate at which particles will be stretched, based on their movement speed.
UV Animation	If either of these are set, the UV coordinates of the particles will be generated for use with a tile animated texture. See the section on Animated Textures below.
X Tile	Number of frames located across the X axis.
Y Tile	Number of frames located across the Y axis.
Cycles	How many times to loop the animation sequence.

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Vivek Shah 
Game Developer in Unity3d