LED driver -  There is two main types of LED Drivers, Constant current drivers - which will provide you with a fixed output current, Constant voltage LED drivers - Which will give you a fixed voltage, the Constant current is typically used when trying to control the Lumen output on a fixture, the constant Voltage is typically used for a fixture that needs a stable Voltage, it will usually be 12 or 24 Volt.

LED Driver Features - Here is what you need to look at when buying an LED Driver.                                                                                                                         

Wattage - Although the Wattage will not control the Lumen output the higher the Wattage is on a Driver it will usually have a higher output Current.

Programmable / Output Current - While some drivers have a fixed output current that controls the mA, that s good if you know exactly which fixture your going to use it for and exactly how many mA you need to light up the fixture, if you dont know that yet a Programmable LED Driver is a better option, they will typically come in a range of 400/1400mA and you will be able to control that with either a programming tool or with some feature on the LED Driver.  

Voltage - Is the fixture going to be used in a 120 Voltage building or 277 building, most LED Drivers will be 120/277V.

Dimmable - Dimming is a huge part of LED these days, it gives you flexibility to set your Light Fixture to your comfortable level at any time of the day, but they also play a big role in Energy efficiency to save on your Electric bill and help the environment at the same time by using less electricity. As technology evolved most Dimmable LED Drivers are now dimming down to 1%