how to use dc motor with arduino

I want to use a normal DC motor with my arduino mega but I don't know how.
I would be really happy if you help me... thanks

What is a normal DC motor?
What voltage and current are you considering?
What do you want the motor to do?
What is your background?

I just want to give my motor a program. for example I wanna turn it on for 3 seconds and then turn it off for 2 seconds.
I think I have to tell you that I know C++ but I'm new to arduino.

What motor do you have?
Do you want to be able to reverse the motor rotation?

Try reading this:-

What do you mean by a "normal" DC motor. One that isn't abnormal?

Hint: use numbers/voltages/currents/datasheet links/part numbers to describe things,
not adjectives, then we'll know what you are talking about. DC motors come in many
flavours, we'll guess you mean a brushed permanent-magnet DC motor, but they
come in all sizes and you haven't given any clue about power/size/current/voltage.

Once these figures are known possible motor drivers can be suggested.