You can not "control" a standard DC motor directly from the Pi.
If you connect a standard DC motor to the Pi's 5V and ground pins the motor will be running at a fixed speed, in a fixed direction, for as long as the Pi is powered. Even this makes the gross assumption that the 5V pin is high enough in voltage and can supply enough current to move the motor at all.
By control we mean you can set the motor on and off, affect its speed, and change its direction.
For this you need a motor driver board (and normally an external power supply).
The motor driver board provides the control functions to the DC motor. The Pi controls the motor driver board using its GPIO.
Popular boards may be bought quite inexpensively (e.g. a few UK pounds from eBay). Look for L298N, L9110S based modules. You can even use a motor driver chip on a breadboard (e.g. a L293DN).