Need explanation

[Bruce]

i need help. can you please give me just a slight idea how scrolling led works?

Individual LEDs or LED displays?

why do we need decade counters?

1. People can't count that high without removing their shoes.
2. Folks are too busy to count for 10 years, so they hire a decade counter.
3. It's an easy job for old cousin Earl with nothing better to do for the next 10 years.
4. Electronic counters.

Just kidding...;o}

Here's a few examples;
http://www.doctronics.co.uk/4017.htm
http://www.hobbyprojects.com/digital...e_counter.html

whats the concept behind why characters are being displayed

What type of display are you refering to?