adding links to main page within a post

Hi,
I installed WP 2.02 and I love it. One thing I can’t fingure out though is how to add a link back on my individual posts. For example. I write a post and assign it to a category if someone clicks on that category and sees the post in there they have to hit the back button to go back to the main page. I would like to be able to have a link on all of these pages that links to the main index.php page. Is there a way to do this automatically or will I have to insert an link in each post for that?