If you're talking about building a spreadsheet to submit orders to your trading application, obviously that will be specific to the application you are using, but the application itself should have examples of the format in excel that you need to use.
If you were just talking about how the futures relate to the expected opening price, then Don's example a few posts back should clarify that for you.
If you are referring to envelope size, that is basically a personal preference that comes with experience. Some use large envelopes, some use small. Some people keep the same envelope no matter what, others like to change envelopes based on how big a gap open there will be. That is pretty much a trial and error process but very much tied to your own risk tolerance, and not to any set of rules.
Hope this helps.