They probably have a drain that leads outside, like how some types of window do.

T156 is right, most of the time there is just a catch pan and a drain pipe that dump the water somewhere else.

For more detail, condensers and evaporators get their names from what is happening to the refrigerant in the system. In the summer, the evaporator (inside) will get cold and cause water condensate to form, coming from the air.

This video by Technology Connections is one of the things being referenced in this thread. I haven't seen this one specifically, but he is very good at breaking down topics into pieces that slowly build on each other.