Step 1: Motor H bridge
As for the inputs should be connected to arduino digital pins go for alternate pins like 2and4 and leave pin 3 for the enable pin. For forward motion set input pin 1and3 high and the others as low also set enable pins as high . Do just the reverse of it for back motion .
Enable pin will set the state and speed of the motors connect it to pin 3and5 . Always set the enable pin to high to get the motors running.
To see an example of how to get the motors going and code check my other instructables