The recipes that you follow instruct you to cook food for a certain amount of time at a certain temperature; they assume that you are not going to place the food into a cold oven and then turn it on -- you are going to preheat it. This is why the first step in almost every recipe is an instruction that tells you to preheat the oven to a specific temperature. Preheating a Whirlpool oven is not a complicated process.
Press the "Bake" button on the oven's control panel. The temperature "350" will appear on the display. If this is the temperature to which you want to preheat your oven press "Start," otherwise move on to Step 2.
Press the "+" button under "Set Temp/Time" if you want to increase the temperature from 350 degrees Fahrenheit. Press the "-" button if you want to decrease the temperature from 350 degrees Fahrenheit. Press either the "+" or "-" button one time for each 5 degrees Fahrenheit you want to adjust the preheating temperature.
Press "Start." The oven will beep when it reaches the preheat temperature.