Oahu’s public transit system is called The Bus. It may not be the quickest way to travel, but it will take you all around the Island.
In March 2022, they introduced the HOLO card which is a contactless smart card used to pay for public transport fares on the island of Oahu. The Holo card is used by tapping it on a reader terminal when boarding TheBus, and can be loaded online at the HOLO card's website, over the phone, or in-person at various retail locations like certain ABC Stores
You can still pay by $3.00 cash for a single adult fare and $7.50 for a day.
This is the cheapest way for you to travel around the island. Make sure you have the exact fare as the drivers don't have change.
You can find further information on the bus website thebus.org or on their app DaBus2
You may like to download the app as soon as you arrive and you'll be able to check the nearest bus stop to your accommodation and also the buses arrival times as it uses GPS.