There are many ways you can use this mechanism, but the basics are pretty simple:
1. You need a thing that can send a signal. Like a door, landing gears or something from a "Sensors and Signals" device.
2. You need something that somehow follows that signal.

Now, get yourself

• "Sensors and Signals" and
  
• "Lights"

• Put them both in your belt
  
• select the "Sensors and Signals"
  
• right-click, so you see what devices you can create here
  
• select "Lever" for this example
  
• install the lever on a wall (or window)
  
• target the lever with the cross-hair of your mouse
  
• press 'p'
  
• Switch to "Devices"
  
• The new lever should already be selected
  
• Now one of the important facts: you should put everything you want to send or receive signals into a group. Why? It is a secret! It is so much secret that I don't know the answer why some things are not possible if the device is not in a group. So.. shoo, now we share a secret. Pinky finger and all!
  
• Create a group "Signals" by pressing the button with the "+".
  
• Select your new lever and press the button "Add to group" and select your new group "Signals".
  
• Now, with the lever still selected, switch to the tab "Signal Logic".
  
• Behind "Tx Signal" you now add "txMyPinkyLever". You know how to keep your secrets!

• Now right-click your light in your belt
  
• Select "Light 1" for this example
  
• Install the light near the lever
  
• Point your cross-hair at the light
  
• Press 'p'
  
• Put your light into a new group "Test"
  
• On the tab "Signal Logic" select your test light and look at the middle panel
  
• Configure Signal: On/Off: txMyPinkyLever / Follow

• Test, if the lever toggles the light
  
• If no, YOU DID SOMETHING WRONG! Yeah, really. Chances are you skipped something somewhere.
  
• If it works, you just used the most simple logic from "Signal Logic".
  
• Now try to activate a teleporter with a motion sensor (one of the "Sensors and Signals" choices).
  
• Disable your engines if at least ONE of the landing gears is activated.
  
• By now you probably have a lot of ideas what you could try.