In Unity, a particle system is a powerful tool used for creating various visual effects such as fire, smoke, explosions, rain, sparks, and more. It's essentially a collection of small, simple objects (particles) that are generated and controlled dynamically to create complex effects.

When we create a particle system this is it’s interface in the inspector

Key properties:

Lifetime: Determines how long each particle exists before disappearing. Specified in seconds.

Start Color: Defines the initial color of particles when they are emitted. Can be a single color or a gradient, allowing for smooth color transitions.

Start Size: Specifies the initial size of particles upon emission. Size can be uniform for all particles or randomized within a range.

Start Speed: Sets the initial velocity of particles when they are emitted. Determines how fast particles move away from the emitter.

Rotation: Determines whether particles rotate and how they rotate over their lifetime. Rotation can add realism to effects like smoke, fire, or debris.

Emission

Rate Over Time: This property controls the number of particles emitted per second.

It's a straightforward way to adjust the density of particle effects.

For example, setting a rate of 10 particles per second means that every second, 10 new particles will be emitted from the emitter.

Bursts: Burst emission allows you to emit particles in bursts rather than continuously.

You can define specific intervals during which a large number of particles are emitted all at once.

This is useful for creating effects like explosions or sudden bursts of sparks.

Shape

Common Emission Shapes:

Point:

• Emit particles from a single point in space;
• Useful for creating effects like sparks, magic spells, or single-point explosions.

Sphere:

• Emit particles from a spherical volume;
• You can control the radius of the sphere, allowing for effects like smoke plumes or explosions that emanate outward in all directions.

Cone:

• Emit particles in a cone-shaped area;
• Parameters such as angle and length of the cone can be adjusted to control the spread and direction of particles;
• Useful for effects like gunfire, rocket thrusters, or directional sparks.

Box:

• Emit particles within a rectangular volume;
• You can specify the dimensions of the box along each axis, allowing for precise control over the shape and size of the emission area;
• Useful for effects like rain, snow, or debris falling within a confined area.

Mesh:

• Emit particles from the surface of a 3D mesh;
• Allows for more complex and customizable emission shapes based on the geometry of the mesh;
• Useful for effects like sparks emanating from a metal surface or leaves falling from trees.

Additional Options and Parameters:

Randomize Direction: Some emission shapes allow you to randomize the direction of emitted particles, adding variation and realism to the effect.

Spread: Controls the spread or divergence of emitted particles within the shape. Higher spread values result in particles being emitted in a wider area.

Controle particles with script:

In the Start() method, the Play() method is called on the my_particles ParticleSystem component, causing it to start emitting particles. Immediately after calling Play(), the Stop() method is called on the same my_particles ParticleSystem component, causing it to stop emitting particles.

This is the official documentation from unity about the particles system: Particle System