I am devising a knock lock for which i used a bipolar stepper motor using a mosfet driver..I have four terminals coming out of motors! I connected them all with four mosfets...Now it doesn't move...so I did a small research on internet on bipolar stepper motor drivers and i got these circuit diagrams in which they connected the motor with MC driver as I did but the coils are also coonected to 12 v from their middle...
From where should this connection be made..??? We have four terminals coming out of motor which are all already engaged completely... So how will this 12v battery connection to motor made?

 

The diagrams you've been finding are for "unipolar" stepper motors. Unipolar stepper motors generally have five or six wires; the two internal windings are center-tapped.

Bipolar stepper motors only have four wires; they do not have the center tap.

You will need to use a dual H-bridge configuration to drive your stepper motor.

Look at the L297 and L298 bipolar stepper motor drivers; you use them together. The L297 is the control IC, the L298 is the H-bridge driver IC.