How do I change my computer from saving the file as an excel?

I am so frustrated! Every time I have saved a document to my computer, libre office opens it in an excel file when it is not an excel file. I also saved a file in RTF for my online college class and it changed it to excel settings when I typed it in the text file type. What is going on??? Is it my default settings? Please help!!

Settings for LibreO on my Ubuntu system are found under TOOLS > OPTIONS > LOAD/SAVE. ( Other systems may use other menus to reach the LOAD / SAVE options.) Go through the LOAD / SAVE options to make certain that the ones you prefer are selected. We normally advise that you import, created and store the date as native ODF files, .odt for writer, .ods for spreadsheet etc. Convert to EXCEL RTF only on exporting the file elsewhere.

I hope this is the problem you are describing…Peter