It states that induced emf opposes the cause due to which it has been induced.
Consider the following examples.
(a) Suppose north-pole of a bar magnet is moved towards a loop as shown in the figure.
Because of change in magnetic flux associated with the loop current is induced in it. Due to induced current magnetic field is induced in such a way that it opposes the motion of bar magnet.
As north pole is moving towards the loop hence to oppose the motion of the bar magnet only north pole will be induced on that face of the loop which faces the magnet. Hence the induced current will be anticlockwise.
(b) Consider the figure shown.
A rectangular loop ABCD is being pulled out of the magnetic field directed into the plane of the paper and perpendicular to the plane of the paper. As the loop is dragged out of the field the flux associated with the loop which is directed into the plane of the paper decreases.
The induced current will flow in the loop in the sense to oppose the decreasing of this flux. For this to happen magnetic field due to induced current in the loop must be directed into the plane of the paper. Hence current in the loop must flow in the clockwise sense.