What kind of motors are you talking about? brush DC motors or steppers?
It also depends on the type of controller you purchase. Some are "4-wire controllers", most are "2-wire controllers" which use 1 PWM pin to set current level in the motor and use another pin to set motor direction. To hook up 4 DC motors you would use 4 PWM pins and 4 non-PWM pins (they don't HAVE to be non-PWM pins, but they don't need to be). The remaining details really depend upon which motors you're using, their current levels, your choice of controller, etc.
FWIW, we have some instructions on rewiring our Rugged Motor Driver
to allow you to stack up to 3 drivers on an Arduino to control up to 6 DC motors or 3 stepper motors.
: compatible with Arduino UNO, 24V operation, all I/O's fused and protected