Making changes to existing page - how do I make a draft page first?
After Step 3, you can hit Ctrl+S (windows) or Cmd+S (macOS). That will just save that update to the entry as a new draft. 

Though Craft 3 brings autosaving, I'd still recommend you to use these shortcuts to save the draft. 

When that particular draft gets approved, go back to that draft and hit on the big red Save button at the top-right corner. You should see another Save as a Draft grey button before that bit save button. 

Current button drop-down shows the document's version history - as in who worked on that particular entry along with the timestamp.