Right Usage of Canonical Tag

[jatinder]

I dont know how to use canonical tags. My website has two urls like <!-- m --><a class="postlink" href="http://www.example.com">http://www.example.com</a><!-- m --> and <!-- m --><a class="postlink" href="http://www.example.com/index.php">http://www.example.com/index.php</a><!-- m --> . I prefer to only .com domain, not to index.php. I want to put a question in this case, on which page I have to apply canonical tag? Please answer me very soon.