Logic Gates are virtual electronic gates which perform operation on binary bits as per their predefined function.A logic gate as many inputs but one output only. Truth Table is tabulated form of output conditions for their respective input conditions for a logic gate. Truth Table is formed by filling all possible input conditions in input columns & for each combination of input, output is
. calculated from equation or circuit and filled in output column. Truth table of a Logic gate reflects it's behavior. You can find more information here: http://en.wikipedia.org/wiki/Logic_gate