How do I download stuff without having to pay ?

Go to the App Store, tap the round blue "person" icon in the upper right corner, then select "Purchased" and you'll see, and be able to download, all the apps you've ever had. You may need to log in with your Apple ID.

You generally need to have a payment method on file to download apps, even if the apps are free, or you have already paid for them, and they are available in your purchase history.