To filter data in Excel online: 1) Upload your Excel file (.xlsx, .xls, or .csv), 2) Select the worksheet if multiple sheets exist, 3) Drag column headers from "Original Headers" to "Selected Headers" to choose which columns to include, 4) Reorder columns by dragging them within the selected area, 5) Click "Generate Preview" to see filtered data, and 6) Export the filtered Excel data as CSV. Our Excel online filter tool processes everything locally in your browser for security.