If you want to save just "Excel files" or just "Word Files" to a SharePoint Library, then multiple file formats must be considered. Excel has several formats and so does Word although below are the most common types that you are likely to receive by email.
MS Excel = .xlsx, .xls, .csv (and others)
MS Word = .docx, .doc (and others)
When using "Dynamic content", a common way to get the file name is to use "Attachments name" from the "Get email" action. This is great and very simple, but what if you already have files of the same name in that location?
The answer, it will overwrite the old file. This may be what you want and if so great, but what if a system generates a file called "report.csv" every day and sends it to you. You may want to keep a hold of all the reports.csv version that arrive daily.
Wouldn't it be better to save reports.csv as reports-2019-03-08-19-15-20.csv so that each new version doesn't conflict with the last?
This is ultimately what we will achieve in this how-to Flow blog post.
The method I will now step through triggers on receipt of a new email, captures the file format then adds a time stamp to the end of the file name on save.
Here is the completed Flow.