Mini-Sheets Paper Size, 2160, 2163, 2181

The paper size is 4.25" x 11".  You might need to enter this size in your printer's Properties or Preferences.
Use the bypass tray or manual feed tray in your printer.  Slide the paper guides so they snugly hold the sheets in place.  Test first on a plain sheet of paper cut to 4.25" x 11" to confirm the design and the feed path.
If your printer has an envelope feed feature, that should make it easy to print these products.