Pellet grills are closed barrels that work on the same principle as an oven, with hot air cooking the food by means of convection.
An automatic auger system conveys the pellets from a storage container (hopper) to the combustion chamber. After the pellets are lit electrically by a special igniter, the smoker adjusts the speed of the pellet feed and/or airflow from the fan until the set temperature is reached. On a charcoal grill, all this needs to be done by hand. But pellet grills perform the same operations automatically, thereby cutting down on all those fiddly adjustments and settings.
The temperature is consistent over the entire cooking surface thanks to the airflow from the fan, which doesn't just heat up the fire plate by generating vigorous flames but also circulates the hot air, as in a fan oven. The deflectors will also help to distribute the heat properly, and will prevent any contact between the fat from the food and the fire plate. The fat drains into a bucket that is designed to make cleaning easier.