DESMOS Activities
According to Yanabh Desmos from the Desmos Facebook Discussion group [image cite] desmos does not recommend embedding - they prefer that students complete the activity w/in desmos. So this is recommended.
If you just want students to experiment with a manipulative... then you could embed it.
Get a Single Session student link
https://student.desmos.com/join/kwczbp

Use Iframe Generator with that link to create and embed. Note - students will have to cotinue without signing in.
<iframe src="https://student.desmos.com/join/kwczbp" style="border:0px #ffffff none;" name="myiFrame" scrolling="yes" frameborder="1" marginheight="0px" marginwidth="0px" height="500px" width="1000px" allowfullscreen></iframe>