For the output Y to be high (a logic state 1) both input A AND input B needs to be high.

The truthtable below shows that this is the case:

n-input gate

You can have any number of input lines into a gate. To give a high output ALL must be high.

Boolean Expression for the AND gate:

Y = A.B

Switch circuit equivalent

To help you understand what an AND gate does we can consider a simple electrical circuit. When the switch is open the state of the gate input can be thought of as being low (0), when it is closed the gate input can be thought of as being high (1).

When the lamp lights up the output state is high (1) and when it is unlit the state is low(0).

As this is a series circuit both switches have to be closed to light up the lamp.