Using led drivers have two primary purposes: To convert high AC line voltage to low DC voltage, and to fix the electrical current to your light fixture.
In simple terms, current is the rate of electricity that is flowing into your light (measured in amps). Too little or too much effects the light output and reliability of your LEDs. A constant current led driver makes sure that they have just the right amount of electricity flow necessary. Not too little, not too much. Just right.
Constant current LED drivers also have the flexibility of being able to adjust the voltage as needed. As you add more and more LEDs, the output on the driver will incrementally increase up to the maximum voltage.
Usually, the manufacturer of the LED light will indicate which type of power supply you need. However, you may also be able to check the fixture itself to see how it is rated. If it's rated for milliamps or amps (mA or A), you are in the right place. If it's rated for a specific voltage, you may need a 12 Volt or 24 Volt constant voltage driver.