Use the External Content block to embed content from a URL into your message.
In Salesforce Marketing Cloud Content Builder, how do I add an External Content block?
Hover over and click on the Layout to edit. In the Block tab, drag and drop External Content to the area where you want it to display.
The Content block opens for editing. In the left-hand pane under Content, enter the complete URL of the content you want to embed.
Under Retrieval Method, select
Immediately: The URL content will be retrieved at the time Immediately is selected. This content can be edited.
Send Time: The URL content will be retrieved when the email is processed for sending. This content cannot be edited.
Under the Block Settings tab, add Background, Border, and Spacing as desired.
When finished, click Done Editing.