Paste the iframe code in the template.
Code looks like this:
<iframe src="https://streetmix.net/-/309795" width=100%; height=600px></iframe>
Be aware that if you are embedding a person's post - people will not be able to see it unless they are friends with that person. If you have permission from the person, you can download any photo and put that in the post (like any other image) and add any text that goes with the post instead of embedding.
To embed a post - see below:Read more