Personally I find that the canonical tag is a pointless tag to use and for the issues it has already caused many webmasters I'd suggest to stay right away from since you can achieve the same result from consistent href formatting, robots.txt, and webmaster tools. Others may have a different opinion.
yes its simple..just any other tag attributes... Learn more about canonical here: http://www.google.com/support/webmasters/bin/answer.py?hl=en&answer=139394
if my page index like this then canonical Tag needed or not? www.mysite.com/abc.html mysite.com/abc.html this type of both page index in google then it needed or not?
No, canonocal is not needed. For example - If you have www.mysite.com/index.html and www.mysite.com/default.html and www.mysite.com/index.htm; all of those pointing to the same start page on your site, then and only then canonical tag is important and required.
Either that or use Google webmaster tools to set a preference which gives the same result without the use of a .htaccess file.
Google webmaster tools cannot able to set the this setting.. i see this message when i try Part of the process of setting a preferred domain is to verify that you own http://mysite.com/. Please verify http://mysite.com/