The following are the steps to add social bookmarking and share button to your website:
1. Go to AddThis.com
2. Select button and click yes if you want analytics, then click Next
Note : If you want to customize your button just click "Get AddThis"
If you want to add the widget in every post just follow these steps
1. Login to Blogger
2. Click "Design" then check "Expand Widget Templates"
3. Find code as shown in this picture below and paste your widget code below the code.
4. Click Save Template
If the widget successfully installed, the widget will display as shown below