how to open excel files on mac

One option is to use Apple's Numbers app. Open Numbers and then go to the File menu, click Open and navigate to the Excel document. Or you can first find the document via Finder and then use the File menu Get Info (or command i) and in the Open With section of the Info window, change it to Open With: Numbers.

Depending on the complexity of the Excel file, Numbers may or may not translate everything well.

Other options are to either buy or license Microsoft Office for Mac: https://products.office.com/en-us/mac/microsoft-office-for-mac

or download the free LibreOffice which is very compatible: https://www.libreoffice.org/

You can install Microsoft Excel (as part of Microsoft Office for Mac) via the Microsoft Store.

You can also install Apple's Numbers.app (from the App Store) which can open Excel documents.

If you just need to view the document, then Mac OS X can preview (but not edit) documents via Quick View with no additional software needed.

You can use Excel for Mac (best) or Numbers (not best), Libre Office and Open Office are other choices, both are much closer to Excel than Numbers.