Just to backtrack for a second, everyone knows that the transformer supplies the electrical power to the track via a physical connection to the track, itself, using a variety of connection methods - such as lock-ons, soldering, barrel connectors and the Quick-disconnect Fastrack connectors shown by Leo, above.
What some people, especially people new to the hobby, may not realize is that just one physical power connection to the track from the transformer may not be enough to sufficiently power your track, depending on the size of your layout. For very small layouts, one connection may be enough, but anything beyond a very small single loop of track will probably require at least a second or third, etc. connection point.
The reason is that there will be some voltage loss the further down the track you get from the point where you have made your initial power connection so, although the voltage may be good right there, it may not be high enough further down the track to effectively run your train, especially if you are using lionchief engines which run best with a rather high constant voltage. This typically shows up when your train runs at one speed near the initial connection point but starts to slow down or hesitate further down the track.
The solution is to make multiple power connections (drops) from your transformer all along the track, about every six track joints and the easiest way to do this (IMHO) is to use the MTH terminal block shown above to connect your transformer to and then run multiple connections from the terminal block to various locations along your track using the connectors shown above. That will provide multiple power drops to even the furthest point on your layout.
Hope this helps explain what is going on.
Note: We are talking specifically about wiring Fastrack - obviously, you can also use a bus wiring technique with feeders to accomplish a similar result.
