How to know where to place a block in the body of my page
If you're new to Drupal 7, I also encourage you to look into placing your blocks using the Context module, rather then hard-coding their location through theming or something like that.  It's also more flexible than what you can just do through the block admin interface.

Here's a simple example of using the Context module to place a block in a certain location on a single page or a specific content type:


Once you've downloaded and enabled the module, go to admin/structure/context
Click the "Add" link to add a new context
Fill in the first few fields as shown below (name, tag, conditions to be met to fire this context)





Before saving, in the "Reactions" section, select which blocks you want displayed and WHERE when the conditions above are met