How do you pay for a secured credit card?

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I was researching secured credit cards for my boyfriend. I never heard anything about secured cards so I have a stupid question. If you pay and put money on the card, how do you pay it off every month? Do you need to keep a certain balance on it like $500? Does it work backwards from a regular credit card? So if you spend $250 on it you have to add another $250 on it? And how do they calculate your APR and interest? I know the fees are high, but it seems like the only alternative to improving his credit.

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So when people say to pay it off, do they mean pay to get back to the balance and they get their deposit back?

i mean if they wanted to close it, do they get their original deposit back?

bdancer- But do you get that collateral back when you close the card?

How do you pay for a secured credit card?