https://teachercenter.withgoogle.com/gettingstarted/week8/topics#4
IMPORTANT: You DO NOT have to modify where the links go to if you like them the way they are (they already go to the right places!)
IMPORTANT: Make sure you set the appropriate sharing settings in any files you want to embed. If the document needs to be available without signing in, make sure its shared publicly and has the appropriate editing permissions desired (edit, view only, etc.) Vice versa, if you want the document to be restricted to signed in users only, the embedded file will still be embedded but will be "locked" behind a sign in screen unless the user is signed in - see the Google Slide example below.
Content that can be downloaded and viewed offline. Examples might include things such as a printable PDF of the same assignment(s) posted in Google Classroom for offline completion.
Google Sites makes it super easy to embed a PDF from Google Drive, or a Google Doc/Slide/Sheet here.