session_start()

Question

why session_start() must be returned first?
what happens if I write it after some steps?

Answer 1

Session must be initialized first prior to ANY output, failing to comply with this requirement will prevent the php code from executing smoothly. More details over what happens if we don't do it right may be found on this discussion:

https://stackoverflow.com/questions/7432235/problem-with-session-start-function-session-start