Samsung ML--6100 - Manual (Page 21)

2. 4 Printer Setup
Loading Paper into the Cassette
You can load approximately 250 sheets of paper in the paper cassette. If
you purchase an option cassette and attach it below the standard paper
cassette (see ‘Option Cassette’ on page 6.14), you can also load paper in
the option cassette.
The window on the front of the paper cassette shows the amount of
paper currently left in the cassette. When the cassette becomes empty, the
window turns into red.
To load a stack of paper:
1. Remove the paper cassette by pulling it toward you.
Paper full Paper empty
2. Press the bottom plate until it locks into place.