Hello farooq;
I am sorry if I was unclear.
There are videos on S7-300 that you can locate by yourself on youtube, they can be enlightening.
The link I proposed is to a series of S7-300 tutorials developped by Siemens, with explanations an the different aspects of PLC programming, with available sample program downloads to help develop you own skills.
Hope this clarifies things,
Daniel Chartier