that question is rather vague. you're going to need to go into more detail. I'm assuming you want different SIDs based on different conditions? what conditions? the more you tell us the more we can help.
Just add the ?sid=1234 to the end of your links. If you want to know how to create a full visitor tracking system thats another question.
I am planning to start an incentive website and I want to track whether they really complete the lead before getting a reward. They should enter their payment ID number and click next which will display the banners of advts. When they click the banner, the payment id should be added to the link of clicked banner so that i can reward them with incentives.
Just create a table where the users all have a unique ID number. Append the ID number as the SID and you can track it from there.