Cup holders are designed to securely hold cups or beverage cans.
With manual transmission: Open the lid to use the cup holder.
With automatic transmission: Press the lid to use the cup holder.

To ensure that cups or beverage cans are held securely, adjust the size using the adapter.
The rear cup holder is located in the rear armrest. Lower the armrest to use the cup holder.

Source: http://carmanz.info/toyota/camry-2001-2006/227522-tc200188.html