Adriana's got it.
You can post the widget code into an HTML/text widget, into a post, or insert it into your themes's HTML.
What blog platform are you using?
For adding widgets to blog posts: Most blog platforms (like Wordpress, Blogger, Livejournal) have two tabs at the top of the post editor. One is the Compose/Rich-text/visu al tab, and the other is the HTML tab. Click on the HTML tab of the post editor, then paste your widget code into there. You can add text or other content around the widget if you like, too.