Samsung SCX-5639FR-XAA - Manual (Page 51)

Media and tray
51 2. Menu overview and basic setup
 
4
Loading paper in the tray/optional tray
1 Pull out the paper tray.
2 Flex or fan the edge of the paper stack to separate the pages
before loading papers.
3 Place paper with the side you want to print on facing down.
4 Slide the paper length guide until it lightly touches the end of
the paper stack.
5 Squeeze the paper width guide and slide it to the edge of the
paper stack without causing it to bend.