Baking is the technique of prolonged cooking of food by dry heat acting by convection, and not by radiation, normally in an oven, but also in hot ashes, or on hot stones. It is primarily used for the preparation of bread, cakes, pastries and pies, tarts, quiches, cookies and crackers.
You should preheat the oven for at least 10 to 15 minutes before starting to bake. Oven temperatures can vary from the dial settings by as much as 50 degrees, so you may need to check the temperature with an oven thermometer.
Selecting the baking sheets for cookies
Use flat baking sheets or those with very low edges. The shiny, heavy gauge aluminum is best for cooking cookies, but there are the dark cookie sheets that may cause excessive browning. For best results, the cookie sheets should be 1 to 2 inches smaller than the oven rack on all sides to allow for proper air circulation.