One of the most important lessons I learned in culinary arts school was how to use a meat thermometer. I never became a world famous chef, not even a regular chef, but I did gain some valuable information about the safety of food. A thermometer is not only important for food safety but taste as well, once I learned to stop over cooking food, I began to get complimented on my cooking quite often.
Using a meat thermometer helps to prevent food borne illnesses, prevent overcooking and will assist you in keeping foods at a safe temperature. When using a thermometer, it is important to put it in the center of the product, not near a bone, or the dish, pot or pan you are using, doing so will give you a false reading.
There are several types of thermometers ranging in price, technology and ease of use. You should also check to see if the thermometer you are buying is for meat or candy, they look similar but are not interchangeable. Meat thermometers usually have imprinted on them a chart showing the different types of meat and what the correct temperature they should be, saving you the time it takes to look up the correct temperature of beef, poultry, pork, etc.
You may choose whatever thermometer you like and that is in your price range, I prefer the instant type of thermometer, they are usually very reasonably priced and can be either digital or mercury type, you simply insert when you want to check the temperature of the food before serving. Oven-proof types of thermometers stay in the meat or casserole for the entire cooking time; they usually have some type of probe to insert in the food and either an analog or digital readout. Some poultry especially turkey have a pop-out "thermometer" inserted for you. Though not really a thermometer, they pop up when the poultry reaches the correct temperature for serving. Regardless of the type of thermometer you use, it is important that it be stainless steel, easy to read and made of shatter-proof material.
For food safety it is important to keep cold foods cold and hot foods hot. After bringing food up to at least 165 degrees F it is then safe to hold most meat, soups and gravies at 140 degrees F. Cold foods should be held at 40 degrees F or lower to protect it from the bacteria that causes food borne illnesses.