The 'HTML' widget allows you to place custom code, or code from a third party, to show content. The 'HTML' widget is found in the upper left.
Once added to the page, you can edit the widget properties to add the customer HTML by following the steps below.
Edit the widget properties by selecting the 'gear' icon along the widgets blue bar.
Paste the custom code into the 'Content' field and select 'Save'.