About oystar card?

I'm in London to study abroad.

I want to make +18 students oystar photocard. I want to ask about it.

If I make it, how can I pay bus fee?

there is zone by bus or all bus is free?

If I make card zone 1-2 and I will go zone3,

can I use top-up function or I have to make another card?

I will in London for 8month. So I want to pay

each month and continue 8month.

If it case, I have to apply the card each month or I just pay each month and I can use same card?

If I can use same card, it will be paid automatically or I will pay in online my self?

Thank you for reading my poor English