This video clip covers the function and parts that make up the mil spec trigger of the AR-15. Schematics and a view of the operation/interaction of parts is provided with a cutaway rifle. PDF instructions also available.
WARNING: Never attempt to disassemble or reassemble a firearm unless you are absolutely certain that it is empty and unloaded. Visually inspect the chamber, the magazine and firing mechanism to be absolutely certain that no ammunition remains in the firearm. Disassembly and reassembly should follow the manufacturer’s instructions.