If you would like to add buttons only to certain posts, pages, custom post types or widgets, then you can use the shortcode. You should to the plugin settings page, unmark all checkboxes in "Buttons" option and click "Save changes" button. Then you should open the necessary post or page in the edit mode, click "Add BWS Shortcode" button, choose the necessary button, click "Insert" and publish/update your post or page.
Please remember, you should manually add the shortcode to every page where you would like to display Twitter buttons.
You can also automatically exclude certain pages or post types from adding the Twitter Buttons. This feature is available only in Twitter Button Pro version. In order to get more detailed information, check the user's guide.