Open the Excel workbook you want to use as the destination
Open the spreadsheet files you want to merge
Copy the data from one sheet
Paste it into the destination sheet
Repeat for each spreadsheet or sheet
Use Paste Special if you need to keep only values, formulas, or formatting
Use Consolidate from the Data tab to combine ranges
Use Power Query to append tables or sheets
Use Move or Copy Sheet to combine entire worksheets into one workbook
Save the merged workbook under a new name