You must speak towards one in order to be heard clearly. Similar to ceiling microphones, placement must be done in such a way as to provide total room coverage without audio problems. An unfortunate side effect is that you must be careful not to trip over the wires on the floor or move the microphones. Most sites have two monitors, one to display what is transmitted and the other to display what is received from a remote site. Some, like CBL, have additonal monitors so that the lecturer can view the remote sites while facing the local audience.
Some sites use a projection system instead of the two monitors mentioned above.
A typical three-color projector is shown at the left. One projector and screen are used to display transmitted or received images.