I’ve heard vague details about the techniques they used, eg using the positions of certain stars, but I haven’t really learned too much about the specifics or scope of these techniques. Also, if you could recommend a book or website where I can find further information I’d greatly appreciate it.
There is an exceptionally detailed answer to a similar question from a year ago by /u/thefairyguineapig: There are huge gaps between islands in the Pacific, what methods did the Polynesians/Islanders use to discover them and to stay on course in a trip between two islands they already knew existed? Do we know how many/what percentage were lost at sea?.
Additionally, our resident expert on Pacific Islanders in general, /u/b1uepenguin, has written a reply to a similar question: How could Polynesians navigate so well without compasses or sextants and how could they build ships capable of traveling deep ocean?.
There's also a bunch of answers to questions about Pacific Islanders and Polynesians in general in our Oceania FAQ if the topic is interesting to you. Happy reading!