How do I use the /particle command in Vanilla Minecraft?

/particle <name> <x> <y> <z> <xd> <yd> <zd> <speed> [count = 1] [mode = normal]

I'll explain all arguments:

• name: Which particle you want to spawn. Here's a list.
• x y z: Coordinates of the particle you want to spawn. (Enter ~ for current position, add a number after the ~ for an offset. Example: ~3 = current position target dimension + 3)
• xd yd zd: Is the area radius you want to spawn the particle in. You can see it as a square: /particle ... 0 0 0 5 5 5 ... spawns somewhere randomly between -5, -5, -5 and 5, 5, 5. Leave 0 for exact position.
• speed: Specifies the speed in a random direction of the particle. Leave 0 for stationary.
• count(optional): How many particles you want to spawn, or in other words: how many times the command should be executed.
• mode(optional): normal or force. This specifies if the everyone should be forced to see the particle. People with the option particles on minimum can't see particles that are more then 16 blocks away, but with force specified it forces the client to display the particle so they can see it no matter what distance.

Example: /particle explode ~ ~ ~ 5 5 5 0.1 100 will generate 100 smoke particles around the player within a radius of 5 at a slightly increased speed of 0.1.

More info here