The white plastic box is the power supply for the amplifier (sends power up the same coax that carries the TV signal). The grey metal box contains the amplifier itself.
On the white plastic box, you should find one port labeled "from antenna". The other port should be labeled "to tv".
Here is an image from a while ago. The ports should be labeled, but maybe the labels are hard to see. Double-check your power supply since things may have changed since this picture was made.
