In a changing magnetic field, according to Maxwell's equations, the changing magnetic field gives rise to an electric field. If there is a loop of wire in this magnetic field then the created electric field will give rise to an induced current in the loop. This current creates a magnetic field opposite the direction of the origional increasing magnetic field within the area of the loop. The direction of the current is found using the right-hand-rule, for example, a current going clockwise creates a B(magnetic) field in, and a counter-clockwise current creates a B field out. As in the picture the increasing B field in created a counter-clockwise current. This clockwise current created a B field out.

Now, what if you have a wire loop in a figure 8? A current going clockwise on the left will go counter-clockwise on the right. The B field will want to make them both go the same way but this is can't happen.