This post may not seem like anything mind blowing, but it is something you might need to know for other things.
When you create a Google Document a UNIQUE code is generated. Clearly the URL for one Google Doc could not be the same as the URL for a different Google Doc, or how would the web know where you want to go?
The unique code is hidden in the URL, it is a long string of numbers and letters (no symbols!)
Sometimes I need this unique code in order to reference to a different document. For example when using the =importrange( formula in a Google Spreadsheet you want to bring one spreadsheet into the other spreadsheet. You will need the unique ID of the 2nd spreadsheet to bring it into the first.
Unique ID for a Spreadsheet
The key is after the key= but before the #gid.
Unique ID for a Google Document
The key is after the slash but before the /edit
Unique ID for a Google Drawing
Same as for the Google Doc, the Google Drawing is after the slash but before the /edit.
Unique ID for a Google Presentation
At the end of the Google Presentation URL is a reference to the slide. The unique ID is in the middle of this long URL. After the slash but before the /edit and slide info.