Visit the button setup page.
Choose the desired button code, such as the 'simple button'.
Copy the code, then navigate to your Moonfruit site editor.
To add the code to your page, click the 'Insert' tab in the main toolbar > 'HTML snippet' in the left sidebar.
In the floating editor, click the 'Setup' tab, paste your code, then Apply and Save your changes. You can review the button by clicking 'View my site' in the top right corner.