If adding an HTML Snippet to your site resulted in blocking your Admin interface, you can remove it by loading the same page with:
?safe_mode=1 parameter after the .html, like:
and then choosing Delete from the blue wrench icon of the faulty snippet.
NOTE: It make take a few seconds (up to a minute) for the page to reload with safe_mode=1.
To add an HTML Snippet reach for the top menu and click Add Content > HTML Snippet. Green rectangles will appear to indicate the locations where the snippet may be added. Click on a green rectangle and the Add HTML Snippet Properties popup will be displayed. Add a Title to indicate what this snippet is for, paste the code into the box and click Add (Update if editing an existing HTML Snippet).
Your snippet may be used to display calendars, polls and other functionalities which are well visible on your page. In this case you may edit the snippet by just rolling over the feature displayed by the snippet. In case the HTML snippet does not have visual repesentation, the location of the snippet you added will be denoted by a small placeholder . Rolling over the placeholder will allow you to access the snippet Edit icon and edit it. Use the Snippet Name field to easily identify snippets without having to open them.
An HTML Snippet may also be added inside the Text and Images editor. This will let you easily position the snippet among your other text, align it, add the snippet inside a table, etc.
You can insert pieces of code into the Head element of your site using the Header HTML feature in Site Properties