First-Time Long-Distance Traveler – Confused About Miles! Help please

Hey everyone!

This is my first time flying such a long distance, and I’m a bit confused about airline miles. I’ll be flying with EVA Air from Europe to Thailand in March, but I didn’t sign up for a miles program before booking.

Would it still make sense to register if I don’t have a travel credit card and don’t fly long-haul that often? Also, can I still collect miles for this trip even though I already bought the ticket?

And one more thing—if I do sign up, can I use the miles with other airlines, or are they only good for EVA Air?

Would really appreciate any advice—thanks!