Popular website CMS tools like Squarespace support Adventr embeds by pasting the URL to the video page.
Instead of copying the Adventr iframe, copy the public URL to your Adventr (e.g. https://adventr.io/campaigns/published/tutorial-01577320).
Then add an "Embed" block on Squarespace and paste in the Adventr URL.
For other HTML websites, you may need to use the Adventr <iframe/> embed.
If you need help finding where you can insert code into your website CMS, ask your web designer.