Using a Self Cleaning Oven Without Instructions

Mine has a clean button on the oven temp dial. You need to lock the lever in the front shut, turn the dial. It will automatically unlock after it is cool enough. Takes about 4 hours. Then wipe clean with warm mild soap water.
Safety issues: Make sure there is nothing near the stove that could combust. If you can, pull it away from the wall abit. More air around it will help with cool down, if you have wall paper on wall, will help keep it cooler.
I use mine about once a year. I do not broil in my oven, use the outdoor grill. Saves on alot of cleaning.

With my whirlpool oven, I just push the button and set the length of time if I don't want a full clean. The door is then locked until the timer goes off. The smell isn't all that bad, but then I run it when ever it gets anything in it.

I have also had success in Googling the model number of an appliance, if you can find it on the inside door or someplace, and you will often find websites that have your particular model's manual available online.

If your oven is really dirty and greasy you may want to clean it first with oven cleaner. If you turn on your self cleaning oven on when your oven is very greasy, your home will get VERY smokey and your smoke alarms will go off. Plus it stinks!

You didn't list the brand of your oven. In my case I have a GE. I just take anything out of the oven that I have stored there. Once I forgot to do that and melted a plastic cover. Lock the oven door and press the oven clean button. Takes about 4 hours.