How to control 3 12v applications using an arduino? [NEW]

I'm very new to Arduino's and don't have much knowledge on hardware but I'm quite good at software.

I basically want to be able to simple turn on and off 3 different 12v applications individually using preferable only 1 Arduino! How would I be able to do this? It may be very simple but I don't even no where to start.

Thanks

A single Arduino can control thousands of devices.
One way is to use a 4- or 8-relay board.
But we need to know more about the devices if you want the proper advice.
Leo..

How much current does each one need?
A good Logic Level, Low Rds N-channel MOSFET can he used to connect - pin of the devices to GND.

Relays are good too for higher current, non-PWM situation where the switched line needs to be isolated from the Arduino power & Gnd, like switching 120VAC for a light, or high current for a motor that is not being sped up & down.