Number, not number
Since Excel is designed to work with numbers, it assumes everything is a number, or a not-number. Formatting and calculating are much easier if you remember this. You can calculate on dates so those are numbers. You can’t calculate on a word so that’s a not-number. If you’re frustrated trying to get the formatting right, figure out what Excel thinks you’re formatting. If you want to treat a number as a not-number, put an apostrophe in front of the content of the cell (for example, a product number that you would not use in a calculation would be entered as ‘123).
A simple way to know what Excel thinks you’ve entered is to look at the alignment (assuming you haven’t changed it from the default). If it’s left-aligned, it’s a not-number. If it’s right-aligned, it’s a number.