Taking the Bus In Gibraltar - where to do I get tickets for the Government-run bus system?

Hello
I would like to use the bus in Gibraltar to get around, I know it's small but it is also steep. There are two companies, one run by the government, which is less expensive than CitiBus, which is more money however, has a great website and allows for online ticket purchases.
Anyone tell me how I pay to use the government bus system? I would like a one-day all inclusive ticket. Thanks!