You place an ad somewhere in the Internet such on a classified website, on a forum as your signature, on the home page of web directory or a blog that has some traffic.
You pay a small sum for this advertisement.
You are very happy after making the payment because now that you have advertised in the Internet cheaply where millions of people throng and you wait for your telephone bell to start ringing and cash register ring along noisily.
But, oh, does that happen? Invariably not.
I am not saying that no one has read your ad; it was read by at least hundred persons and a few search engines. But how they landed on the page you have advertised? Who read it? From where?
You must necessarily know the answers for these to make the ad work for you. In short, you need an ad tracker.
Get one here.