Faraday's laws tell us that if magnetic flux associated with a closed loop changes then an EMF is definitely induced.By the way do you know that emf is not a physical quantity representing force .It is the work done in moving a unit charge and its unit is volt not newton!.The concept is that changing magnetic flux induces an electric field.

but Sir, how can we have electric field without charges.

That is a good question ! .the electric field due to stationary charges has some additional features .Like line integral over a closed path is always zero.For the time being let us ignore the difference.

OK ,changing flux induces a current through a loop,but what is the direction.I mean how can we predict the direction.

For that we have a smart law which is indeed very handy for electromagnetic Induction.This law is based on conservation of energy and tells the direction of current induce in the loop.We will directly state the law.

"The emf induced in an electric circuit always acts in such a direction that the current it drives around the circuit opposes the change in magnetic flux which produces the emf. "

This result is known as Lenz's law, after the nineteenth century Russian scientist Heinrich Lenz who first formulated it.

Is that the resaon why we have put a minus sign in the formula EMF = -(dFlux/dTime).d(Flux indicates the usual infinitesimal change in flux).

exactly.So now its time to wind up.Go through your notes at home.