Assuming you have a hitch receiver on your vehicle and the appropriate ball mount for your trailer, there are four main steps to hitching a trailer correctly.
1. Park your vehicle in the position you want it to be in when it's hitched up. You'll want to be sure you have enough room around the back of the vehicle to attach the trailer without hitting anything, and that you're able to align the hitch receiver with the coupler on the trailer.
2. Once everything is aligned, lower the tongue of the trailer down onto the ball mount so that the coupler is fully seated on top of the ball.
3. Use either a pin and clip or a locking hitch pin to secure the coupler to the ball mount. This will prevent it from coming loose while you're driving.
4. Finally, connect any safety chains or cables between your vehicle and trailer according to local laws and regulations. These provide an extra measure of security in case something comes loose while you're on the road.