First, the file type you are using has to support macros. These are: .xls, .xlsm, .xlsb. I used .xlsm for the test file I uploaded. The default .xlsx won't allow macros to be saved as a security feature.

The macros are located in some background area. To see them, you need to go into the VBA editor. By default, Excel hides the Developer tab on the ribbon. Use Alt-F11 for direct access, or go into File/Options and add a checkmark to see the tab.

Once you've done that, then you get a ribbon that looks like this with a Developer tab.

In the VBA editor, doubleclick on This Workbook to see the code I added to the test spreadsheet. To make it run automatically when opening a workbook, the code has to be here. Most other code you create goes into a module. I have a Personal workbook which contains macros I want available for any Excel file I have open. You won't have that.

To add the macro to your own file, you would copy the code and paste it into this section of the VBA editor. Keep in mind every file you have open shows here, so make sure you are in the right "ThisWorkbook".

You can tell Excel which folders are safe so you don't get the macro warning bar (just below the menus). Later versions also allow you to say individual files are safe so the bar no longer comes up.