Canon BJ-20 User Manual page 44

Press the ON LINE switch.
5
The ON LINE indicator lights and the printer is ready for printing.
Cautions
Do not open the paper cover while printing.
Use only paper that satisfies the paper specifications, and
make sure that the paper is not curled, wrinkled, etc.
The paper will curl and may not stack properly if it catches
at the top of the paper cover when being fed into the printer
( as shown in the illustration). If this occurs, slightly tap the
paper with your hand so that it stack properly against the
cover.