Insert and Configure Disqus Code 

1. Sign up for a Disqus account and Login

2. Copy the Universal Code

3. On your new Google Sites use the Embed tool from the right-hand Insert panel and choose the EMBED CODE option

4. BEFORE you finish embedding the code you MUST edit and uncomment the configuration variables (see video for an example)

5. Use  NEXT to preview the code and then  use INSERT to add the code

6. Move and resize the embed code tile to wherever you want on the page.

Full demo video available: Add Disqus Comments - New Google Sites