Where to Add Code for Index/Home Page

I want to insert the code for implementing the AddThis service. But not sure which page in the WP Editor to edit and insert the code.

I know technically, we should not edit any of the .php files.

So please direct me to the page to edit.

I am also trying to add code on this same page for the ‘Who Hit the Page’ plugin. This code is supposed to go into a post area, but the code is showing as text, so I would like to place it directly on the html/template pages themselves. This is the code: [whohit]-Page name or identifier-[/whohit] – but when I put it into the >Display Settings >Home Page >Home Page Text Box and also tried it on other regular pages, the code shows as text.

Please advise on both of these if possible.

Thanx! 🙂
Claudia Beck