There are two main types of digital thermometers used to measure the temperature of a person. The procedure will vary based on the type which you are using.
One type is designed to be placed under the tongue. The thermometer should first be sterilized (by washing then wiping with an alcohol wipe) or encased in a sterile plastic sleeve (if available). The metal tip of the thermometer is then placed under the tongue and the button is pressed. The thermometer will beep when it is time to remove it from under the tongue and read the temperature from the digital display. The plastic sleeve should then be properly discarded (if used) and the thermometer should be sterilized again.
The second type of thermometer is designed to be placed into the ear. The thermometer should be cleaned and sterilized, and a plastic sleeve applied to the tip (if available). The button is pressed and this type of device will also beep when it is time to remove it and read the temperature. Dispose of the plastic sleeve and clean the thermometer.
Please note: Do not share under-tongue thermometers if you don't have the necessary supplies to sterilize them between users. This can spread germs. Alternatively you could rinse with soap and water between users and only hold the thermometer in the armpit to get a reading. This is less accurate but much less likely to spread colds.