Starting from the Basics:

An Overview of Logic Gates:

Logic Gates

A logic gate is an idealized or physical device implementing a Boolean function, that is, it performs a logical operation on one or more logic inputs and produces a single logic output. Either the output is a low state (0) or high state (1). There are different ways of representing the output of the Logic Gates; it may also be in the form of true/false. Basically, a function is assigned to each gate according to their output.

The basic gates are

i)                    AND Gate

ii)                  OR Gate

iii)                NOT Gate

iv)                NAND Gate

v)                  NOR Gate

vi)                XOR Gate

vii)              XNOR Gate

AND Gate:

AND gate works on ‘and’ condition i.e. for two inputs, the output will be ‘High’ if input A and input B both are in ‘High’ state.

The function and the truth table of AND Gate:

                          

AND Gate & Truth Table

OR Gate:

In the same fashion, OR gate operate on ‘or’ condition i.e. the output will be high if either input is high.

NOT Gate:

NOT gate is also known as Inverter. The output is the inverted version of the input.

NOT gate & Truth Table

NAND Gate:

The NAND gate operates on ‘AND logic followed by NOT gate’. When both inputs are high it returns low. It is the reverse case of AND gate. Simply NOT-AND gate abbreviated as NAND gate.

NAND Gate Symbol & Truth Table

NOR Gate:

The NOR gate operates on ‘OR logic followed by NOT gate’. To remember the logic, you may also call it NOT-OR gate.

NOR Gate Symbol, Function & Truth Table

XOR Gate:

The 'Exclusive-OR' gate is a circuit which will give a high output if either, but not both, of its two inputs are high.  An encircled plus sign () is used to show the EOR operation.

XOR gate symbol, Internal Structure & Truth Table

XNOR Gate:
The 'Exclusive-NOR' gate circuit does the opposite to the EOR gate. The result is a low output if either, but not both, of its two inputs are high. The symbol is an EXOR gate with a small circle on the output. The small circle represents inversion.

XNOR Gate Symbol, Equivalent Circuit & Truth Table

Logic gates representation using the Truth table:

All Logic Gates with Truth Table