As a DC user, I believe that I can help. # 205 is a Connector. I use it to control power to separate tracks in a staging yard. Greg's description is correct. It can control power to three separate spurs, or blocks. It is simply a triple off/on switch. It can be used only with a single power source. The #215 Selector (not shown) has power inputs from two power sources and different blocks can be controlled by either power pack. I use them extensively. His description of #210 is also the correct electrical term. They allow for reversing + or - from the same power source to separate insulated tracks. I do not use them, but they can be used as reversers in a reversing loop. It can be used for two track blocks. The @220 is a combination unit, generally used for reversing loops as well. It can also be used for turntables. The green sliding switch overides the directional control on a power supply. I have no personnel experience with this. As Greg posted, the #200 relay is just that. It's basically a switch control motor without the actuator arm. It requires something to activate it, momentary toggle switches can be used, and are a better controller than Atlas switch controllers.
Trailrider's first paragraph is incorrect. None of the buttons on any of the pictured items are momentary switches.
Hope that this helps.
EDIT - All of these components can be wired in series with the same things, using some supplied metal strips. In other words, three connectors can be wired in series to use the same power source to power nine tracks or spurs.
