Log into Blogger and select the blog you want to add AddThis to. Select Design > Edit HTML. These controls look like tabs, and they're located at the top of the page.
Check the Expand Widget Templates checkbox. This checkbox is located in the top right corner of the page, above the code. By clicking the checkbox, the code in the field below will refresh.
Copy and paste the AddThis code snippet into the template, right after the
tag. Note: If you have trouble finding this DIV, try copying and pasting the blogger code into a text file editing program and do a search for 'post-footer'. Once you located it, copy and paste the AddThis button code below the DIV. Then copy the entire text file and replace the code on blogger.
Click Save Template, and you're done! A new page will load along with a confirmation at the top of the page should appear that reads, "Your changes have been saved. View blog." Click View Blog to preview your blog with the new AddThis button. The button should appear beneath each blog post. addthis.com