4 Bit Ripple Counter from T Flip Flops. 

Outputs taken at Q of flip flops.

Observe how all T inputs are tied together. Also there is a common  async reset input for the system.

The Q' output of the fist flip flop drives the clock input of the second input and so on.

Each flip flop has a clock frequency of half that of the preceding flip flop.

This coincides with the pattern for binary counting: 

0000, 0001, 0010, 0011, 0100, 0101, 0110, 0111, 1000 etc