One of the benefits of storing MS Office files on OneDrive as opposed to on a shared network drives is that multiple people can work on editing that same file at the same time. However, this is true only if every person working on that file is using an online/web version of the Office app to edit it, and not the traditional Windows desktop app.
Please note that in order to open a MS Office file with the online/web version of the app, the file must be in the latest format (i.e. .docx, .xlsx, .pptx and not .doc, .xls, .ppt)
MS Excel
When you open an Excel file from OneDrive using the web interface on office.portal.com and click on Edit Workbook, you have a choice to Edit in Excel (Windows desktop version of Excel) or Edit in Browser (online/web version of Excel). Please be sure to use Edit in Browser if you want to allow other to edit this file at the same time.
If you open this file using Edit in Excel option, it will open in read-only mode. At this point, others will still be able to edit it because the file is not checked out on the server:
However, once you click on the Edit Workbook button, this will check out the file on the server and prevent others from being able to edit it at the same time. Anyone who will try to edit a file that was checked out will see the following message being displayed:
For more information, please review the following Microsoft article:
Can I co-author in Excel 2016 for Windows?
MS Word
When it comes to Word documents, as long as you use Word 2016, it is possible to edit the same document by multiple users at the same time in addition to being able to do it with the online/web version of Word.
For more information, please review the following Microsoft article:
Collaborate on Word documents with real-time co-authoring