The large analog window is the main mode of display for weather data. It is split up into sections for each type of data available: time, temperature, pressure, wind speed and direction, humidity, and conditions.
 
By default, the displayed time is that of the current conditions. Clicking within the time box allows you to switch between showing the time of the conditions and the local time that those conditions were downloaded.
The thermometer displays the current temperature, with optional display of the daily minimum and maximum values, and the windchill or heat index, as appropriate for the given conditions. Double-clicking on the thermometer brings up the temperature preferences panel for that city. The arrow indicates the change from the previous reading. This will only appear when there is a previous reading to compare to, so you will not see it when you first start up.
The barometer displays the current barometric pressure, with optional display of the daily minimum and maximum values. Double-clicking on the barometer brings up the barometer preferences panel for that city. The arrow indicates the change from the previous reading. This will only appear when there is a previous reading to compare to, so you will not see it when you first start up.
The wind indicator shows the current wind speed and direction. The black bar points in the direction from which the wind is blowing, analagous to a wind vane pointing into the wind. Double-clicking on the wind indicator brings up the wind preferences panel for that city.
The humidity indicator shows the current relative humidity, with optional display of the dewpoint. Double-clicking on the humidity indicator brings up the city preferences panel for that city.
The current conditions are also displayed, along with a graphic depicting those conditions. Double-clicking on the graphic brings up the local forecast window for that city, if available.
For those who want the data displayed in a more compact form, a "digital" version is available. None of the optional display features from the analog window are available in the digital window.
 
If your desktop space is really scarce, there is also a "tiny" window. Again, optional display features from the analog window are not available.