I want my word processing, presentation slide, and spreadsheet files all to come up in libre office, regardless of the office suite software by which they were originally created. How do I do that?
Might be good next time to say what OS you’re using and what version. If you will do that you have the chance to start to get some points here for your questions.
A simple way is to determine when LibreOffice is installed which file types should be opened by default by LibreOffice. This statement refers to file types of MS Office.
If a subsequent assignment of MS file types to LibreOffice is to be carried out, this can be done in Windows Explorer (OS = MS Windows). See here in the Wiki from TDF.
You did not specify your used OS. If you don’t use MS-Windows, maybe someone else can help you.