How do I pay the game service Steam with a debit card?

I just got a Visa debit card from my Chase bank the other day and I've been trying to use it with Steam and other over-the-internet purchases but it always gets declined. I'm pretty sure I activated it already since I put it in an ATM not long ago. I'm 16 and new to this sort of thing and it would come in handy if I could find out how to work it right. So how exactly do I purchase things like steam games, xbox live memberships, or other purchases online?|||Colaterals and evidence of the finance you have in your Chase Bank.....and the credit limit