There search for head> tag. The easiest way to do it to hit the ctrl+F button and type it and you'll find the tag. After you have located the tag just copy paste the following code above or before the head> tag
<script type="text/javascript" src="http://apis.google.com/js/plusone.js">
After you're done with this, it's time to get the button. For that click here and it will redirect you to the official Google +1 site. From there get the code for the website and paste it in the html where you want to have the button. After that have fun and collect a lot of +1. And don't forget to click on that button below. Happy Blogging :)
For more click on the following links