Buy an Octopus card. You can use it on buses (i.e. those to TKO Industrial Estate, which is not near TKO MTR), MTR including the Airport Express (but it's cheaper to buy from places such as Klook - online & app), minibuses, trams, Peak Tram, ferries, supermarkets, convenience stores... There's a $50 refundable deposit when you buy it (MTR station), and it can be topped up at MTR stations (at counter or machines), 7-11, Circle K, etc. It can also be topped up with a credit card from participating local banks, but you probably don't want the hassle of opening a bank account here, what with US banking regs now applying globally.

To confuse you, Hong Kong uses the international date format (DD/MM/YYYY) and the Chinese date format (YYYY/MM/DD) (since the handover).