php - When do I have to declare session_start();?

Question

So Im a beginner when it comes to PHP so I need a little help. I am trying to figure out when to start the session. Should I do it when the user first registers or what about when they log in?

Also, are sessions 'universal' meaning when I check a session will it work or do I have to include a file to all pages that check if someone has a session?

Answer 1

"Should I do it when the user first registers or what about when they log in?"

You should do it every time you want to get or set any session information. Data stored in the $_SESSION array will only be available after the session is started.

"Also, are sessions 'universal' meaning when I check a session will it work or do I have to include a file to all pages that check if someone has a session?"

Calling session_start() is all you need to create a session. If a session was already created, that session will be used.