I don't understand how to play

On my first playthrough of all Zelda games and this is my last 3d. Love the art style so much.

I've just gotten back from getting the master sword and don't understand how to explore outside the main quests. Every time I try to explore the ocean and pull up to an island that isn't on the main quest, it is either unnacessible or some kind of pirate hold, which i imagine is supposed to come up later.

I also don't understand how to read the Tingle maps. So far, I only have four or five islands uncovered on my map.

At what point am I supposed to start exploring if ever?

Also, how do I get a song to turn night to day and day to night?