Well before you go hooking wires up to any LEDs you should first know a little about electricity. First of all there are two main forms of electricity in commercial use today.
(All of which are dangerous even if you know what you are doing. So with that in mind do not attempt to play with AC current. All safety precautions should be taken before and during working with electricity. If you are unsure what they are. Do not attempt without a skilled professional.)
These two forms of electricity are:
AC = Alternating Current (ie generator)
DC = Direct Current (ie battery)
LEDs are typically 2-12V DC devices, with a few AC varieties. Household electricity is usually provided in 110-120V AC. This calls for an electronic device to regulate the current into a stable predetermined amount while allowing the voltage to fluctuate in response to an increase or decrease of current sensed by the electronics.
If good design isn’t implemented in this LED ‘driver’ circuit then unnecessary waste through inefficiency can occur. To help with such design issues, National Semiconductor has a design tool for use, try it here.