Using a 6" Jointer

Have been using a 6" Reliant jointer ( rarely use it, so better more expensive one not on my list) to smooth edges in order to glue two boards together. It seems the boards are not as smooth as I would expect when butting the boards next to each other. As I stated rarely use it but each time I can never get the edges perfect. Seems like one or both edge is off a bit. I checked the alignment procedure in the manual and tables seem aligned correctly. Maybe I may not be feeding it through the jointer the right way. What can I be doing wrong ? What is the correct way to feed a board edge through a feeder. Do you push from rear or both front and rear?
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