How do automatic train signals work?

Related questions

1. What is signal overlap?
2. What do train lights mean?
3. What does run signal do?
4. What do train whistles mean?
5. Do trains have red lights?
6. How many types of signals are there in railway?
7. Do trains turn around?
8. What is a controlled signal?
9. How does Indian Railway Signal work?
10. What is fixed block Signalling?

Tags

1. #movement
2. #controlled
3. #trains
4. #automatic
5. #working
6. #automatically
7. #operated
8. #these
9. #passage
10. #train
11. #signalling
12. #block
13. #which
14. #system
15. #through
16. #sections
17. #signals