Hi again,
So my boyfriend and I will be in Spain for a month and we will be taking flights in and around Spain (bilbao to barcelona). I'm booking through Rumbo.es and they are asking if I want to charge for my luggage. I don't know if I need to. Is it like the States? We will each have a backpack under thirty five pounds (ish). Should I check the box? Because somewhere I read about being charged more at the airport. Help please!!!!!

If you are using low budget airlines they often have:

1) very tight restrictions on what you can bring on board
2) high prices for extra (or any) checked luggage

Nothing like flying in the US.

You need to go to the web site of the airline and read about the specifics of each one. And they are deadly serious about the size of carry-ons - anything larger they will force you to check at high prices. And even the full service airlines allow only a 19" (not 22" like in the US) and that incudes the wheels. I have seen Americans have to gate-check their carry-ons numerous times even with major airlines.

Go to the airline website and READ the instructions, OK?

If you book with the airlines directly, you'll be aware of all of the additional charges and luggage restrictions.

I refer OP to the definitive text on flying low costs airlines - especially ones with Irish accents

http://www.youtube.com/watch?v=ZAg0lUYHHFc