Arvind,

Please stop using shorcuts ("1" instead of "one"), it is hard to read your posting if you do so (and it is also against this forum's rules).

First, visualise the LEDs inside the 7-segment. One LED in each. If you force some current across it (usually the current is limited using a resistor in series as with a normal LED), it lights up. To spare pins, usually all the LEDs have one end connected together - that is the "common", so if it is "common anode", all the anodes (where you put +) are connected together, and if you put - through resistor on the individual cathodes they will light up.
"Common cathode" is the other way round.



If "1" on the port means that the connected segment will light up, 6 segments will light up (in proper arrangement - connection of the microcontroller pins to 7-segment - it might display "E").

If it is a different arrangement and "0" means that the connected segment will light, 2 segments will light up (in proper arrangement it means "1" displayed).

This assumes 8 segments altogether, most probably one of the output pins would be unconnected.

Experiments often help to understand. Perhaps, if you would take 7 LEDs (take those that have rectangular shape, if you can get them), arrange it in the same pattern as a 7-segment, connect series resistors and a power source and try to light them up manually in the required pattern to display "1", "2" etc., you might get the point quicker.

Jan Waclawek