go for the links
basic knowledge about seven segment
http://www.engineersgarage.com/content/seven-segment-display
7 segment intercaing
http://www.engineersgarage.com/microcontroller/8051projects/interface-seven-segment-AT89C51
user input for 7segment
http://www.engineersgarage.com/microcontroller/8051projects/user-seven-segment-display-AT89C51
seven segment multiplexing
http://www.engineersgarage.com/microcontroller/8051projects/seven-segment-multiplexing-AT89C51
there are number of project given on site which will help you to understand those concepts…. go trough the links i had given above and let us know where exactly you were not able to understand the concept….