This applet simulates what happens inside your house when the temperature and dew point change outside. You have control over the outdoor values by sliding the red colored portion of the two thermometers (one for temperature and one for dew point). The Relative Humidity meter will instantly tell you the value for the outside.
As you change the values outside, your indoor environment is slower to change. If the air is colder outside, your furnace will cycle on and off, keeping the house at approximately the value you set the thermostat to.
Your activities also change change the indoor environment. Select a few of these and look at their impact.
And of course...Have Fun