Can't merge spreadsheets

I need to consolidate two spreadsheets. They were created with different formatting - column names, number of columns, etc. I tried following instructions from https://support.microsoft.com/en-us/office/combine-data-from-multiple-sheets-dd7c7a2a-4648-4dbe-9a11-eedeba1546b4, but I couldn't get it to work. I then created a new sheet and pasting both into it, but that didn't work. My goal is to view all rows so I can see duplicate entries. Please advise. Thank you.