Summarize the following:
Convection oven models are different and these steps may differ from the model that you own. Look for the owners or instruction manual that you got with your convection oven. If you don't have it, use a search engine to see if you can find an online version of the manual. Set your oven to the convection setting by pressing the button or turning a dial to convection. Some appliances will also have a convection bake or roast setting. Use the setting that applies to the food you plan on cooking. If you're making cookies, cakes, or pies, you should set the oven to convection bake. If you're cooking a pot roast or turkey, you should set the oven to convection roast. Since convection ovens cook your food more evenly than a traditional oven, you should reduce the temperature. Look at the recipe that you're cooking and reduce the temperature to 25F (14C) less than what the recipe calls for. Input your cooking temperature into the keypad or turn the dial to the appropriate temperature. Some appliances will automatically adjust the temperature for convection cooking. Refer to the user's manual to see if your oven automatically adjusts the temperature. Some ovens will automatically raise the temperature as you increase it and others require you to hit the "Start" button. After hitting the "Start" button, the oven should begin to rise in temperature. Your oven should beep or an indicator light should come on when it's reached the desired temperature. Your convection should now be preheated.

Summary:
Read the oven's instruction manual. Press the convection button or turn the dial to convection. Preheat to 25F (14C) below the conventional oven temperature. Press the "Start" button. Wait for the oven to beep or for an indicator light to come on.