You can insert Google Docs, Spreadsheets, Presentations, and Forms into either (i) a new page, or (ii) a new post that you have created.
Note: When you insert a Google Doc (or Spreadsheet, etc.), you are actually embedding it. Embedded documents, including Google Documents, don't count against the Sites storage quota. This means that you can embed as many documents as you need to in one page / post without worrying about your Google Sites storage space.
2. Edit the new page or new post.
3. Position the cursor where you would like to insert the object
4. Click on the "Insert" menu and select the item you would like to insert (In this case, insert a Google Document)
5. Choose the document to insert and click "Select"
6. You may wish to change the display settings of the object, then click "Save"
7. A box representing the document (or Presentation, Spreadsheet or Form; depending what you have inserted) should now appear on your page.
8. You may wish to continue editing. Click "Save" when done
9. You will now see embedded document within your page