By default, when you click on a post's link, the post page will load on the current tab/window itself. There are lots of reasons on why you might want your posts to open in new tabs. I won't be discussing what these reasons are (because currently my idle mind can't think of any!), I'm just gonna cut to the chase and show you how.
In this tutorial, I will be using Simple Template by Josh Peterson. It should work with other templates as well, but I can't guarantee on those heavily moded ones. The method remains the same though. If you can grasp the idea, you can apply this simple tweak to your template as well no matter how different it is.