Open both Excel sheets
Check that the columns match or can be aligned
Copy the data from the second sheet
Paste it below the data in the first sheet
Use Power Query to append the sheets if you want an automated method
Use the Consolidate feature if you want to combine summarized data
Use formulas like VLOOKUP, XLOOKUP, or INDEX-MATCH if you need to match records by key
Remove duplicates if needed
Save the combined workbook