The height of the temperature very much depends on the amount of oxygen and other conditions such as wind, humidity, coal type and the outside temperature. So controlling the temperature is almost never 100% the same.
It is not that difficult to achieve a constant high temperature of, say, 250 degrees Celsius or a low temperature of 80-90 degrees Celsius. You can also achieve a constant low temperature for as long as 12 hours without adding new charcoal.
You control the temperature with the top cap and damper. To let the temperature rise slowly, start with the top and bottom vents only slightly open. You can gradually open these a little further and further, to let the temperature rise. The more oxygen, the higher the temperature.
Want to put out the fire? Then you close the top cap and damper. It couldn't be easier! Note: do not use water to extinguish the coals, this can damage the ceramic.
TIP: for slow cooking at a low temperature, always use a plate setter. In that case, don't let the grill get too hot. It takes hours to bring the temperature down again. If you want to bring the temperature down, close the top cap and damper a bit more.