I am taking a general education course on special relativity, and get quite confused by problems asking about which event happens first according to different observers. Is there an effective way to do this?
Let's focus on the following problem:
A train is traveling at constant speed $u$. A, B and C stand inside the train where B is in the middle of A and C. B' is standing outside along the track. Inside the train, A, B and C send light pulse to each other simultaneously at the moment when B passes by B'. Describe the sequence of events (sending pulses, receiving pulses) according to B'.
I get quite confused. Can someone give a hint?