How do u operate a car using overdrive?

I have automatic overdrive on my car that has no switch to turn it on and off. If you have one like that then drive it like you would any other car. If you have a push on, usually located on the shifter itself, simply push it in to use it. It's there to relieve stress on the transmission at cruising speeds and also saves a small portion of gas. And yes, if you're wondering if it's ok to leave it on, it is. I've known many people that have done that and it's perfectly safe.