[0.13.x] Rail Signals

[Overene]

How exactly do rail signals work, and how do I use them? There don't seem to be very many good youtube tutorials. I've so far only figured out how to get an inactive rail signal (where it switches from red, yellow and green constantly) and a constantly red signal, not sure how to get a signal that actually changes though

[Kelderek]

There don't seem to be very many good youtube tutorials.

Try this one:
https://www.youtube.com/watch?v=3ZiL7_vfJtQ

It's a half hour that will turn you into a master user of trains in Factorio. It is the best explanation I have found for everything relating to trains and well worth watching all the way through. It was made back in 0.12, but fundamentally everything is still the same, only some cosmetic changes were added in 0.13.