Canon BJC-250 - Manual (Page 35)

3
Slide in the paper into the manual feed slot on the back of the printer until it
stops inside the sheet feeder.
Align the sheet with left edge of the manual feed slot.
Hold the sheet for about two seconds until it feeds automatically.
The printer will automatically load the paper into position Insert the
single sheet.
After printing on thick paper or envelopes, set the paper thickness lever (inside the printer)
back to the left position before printing on other paper types.