how can I make sure that I have extensions added successfully

You can check your extensions the same way you install them, through the Add-ons manager (get to that through "Extensions and Themes" or by pressing Ctrl+shift+a). Every extension you have installed will be there and whether it's active or not will be indicated by a switch which should be blue. If the extension is disabled, it will also say in the title that it is. Many extensions will also take you to their own website briefly as you install it for the first time. You likely won't receive an email for it from the extension itself unless you've given them your email.