After you have your MailMunch account setup copy the site code from your MailMunch account for your bloggers page.
Now go to your Bloggers site main dashboard and click on the drop down menu in front of your blog and click on Template
Click on Edit HTML
Paste the MailMunch site code you copied earlier before the </head> tag and click Save template. Any forms you have created in your MailMunch account are now live on your bloggers site
If you wish to enable MailMunch for your Bloggers mobile site as well go back and click on Template again and click the gear icon underneath Mobile