Where to place to insert the google analytics Code?

You should add “Google analytics code” in Every page, so that you can get all pages tracking report.
As per google, you should add “Google Analytics code” just before the closing of “head” for better results.

In wordpress, when we are using some theme for displaying your website. there might be textbox in admin section, to add the “Google Analytics” code for tracking purpose.(May OR may not available in your current theme)