If I understand you correctly:
Google refer to standalone and bound scripts. The bound scripts are...bound to a spreadsheet and they cannot be unbound, the standalone scripts are....standalone. (is this what you mean by embedded/not embedded?)
A bound script can allow for some methods in the script that relate directly to the spreadsheet with which it is bound. The one we tend to use the most is:
var ss = SpreadsheetApp.getActive();
which gets the spreadsheet to which the script is bound.
With a standalone script, we will need to specify more precisely:
var ss = SpreadsheetApp.openById('1tKzb0PuqJWsWDSfrTFsqBM60S8n_5ulw48wfRF10SZk');
or
var ss = SpreadsheetApp.getByUrl('https://docs.google.com/spreadsheets/d/1tKzb0PuqJWsWDSfrTFsqBM60S8n_5ulw48wfRF10SZk');
You can use these two methods in a bound script for the bound spreadsheet, or any other spreadsheet.
You should see the spreadsheet ID in the two methods (is this what you are referring to by ID ?) The ID is the unique reference to the file, and can be found in the url address bar when you open a spreadsheet.
Does this answer your queries ?