When viewing the main window of the model (selected by clicking on the "Plot" tab above), you will see a plot and a number of controls.
At the top left is a diagram showing a light source and a thermometer. The thermometer represents some object in a room and which is being warmed by the light source. Arrows pointing to and from the thermometer represent energy being transferred in and out of the object.
Initially the object is in equilibrium with the room, so its temperature is the same as the value (in degrees Celsius, ° C) you have entered in the "Room Temperature" text box in the lower left. When you click on the "Start" buttom at lower right, the experiment begins and the object is warmed by radiation from the light source.
Other values you can enter are the power of the light source are the reflection coefficient (or albedo) of the object, indicating how much of the radiation from the light source it simply reflects; the power of the light source; and the distance between the light source and the object.
You can alter the values in the four text boxes while an experiment is in progress, but doing so will mess up any results from the experiment unless it is your goal to see, for example, what happens if you move the light source or turn it on/off as the experiment is in progress . It's best to stop the experiment, using the "Stop" button, change the values, and then click "Start" to restart.
You can experiment by changing the 1) room temperature, 2) reflection coefficient, 3) light source power, and 4) distance between light source and object. When your experiment is in progress, a graph is displayed at the top right indicating the changing temperature of the object. Pay attention to how the shape of the curve changes as the graphed temperature approaches the equilibrium temperature (which is indicate in the little readout window at bottom center).
In general, when you alter one of these variables, you should leave the other values fixed. This is referred to as a "controlled experiment".