Install BlogThis! Button

Two Methods:

1- You can either get the link and drive it your toolbar from here: What is BlogThis! ? - Blogger Help

2-Or you can add as an Extension in Chrome.  I like this method as the icon sits beside your address bar and doesn't take up space (or move around) like it can on your bookmarks bar.  Get the extension for Chrome here: https://chrome.google.com/extensions/detail/pengoopmcjnbflcjbmoeodbmoflcgjlk