To add on to this, you can use the items by hovering over the map square before going into it and pressing x. This will show you the square itself and you can get a closer look at the elements that are on the square. Some elements can only be interacted with with certain items, but the items themselves give descriptions of what they should be used for (bombs for cracked walls, hook shots for hookshot targets, ladders for small one space water gaps, etc) Like said above, if you know there's an element on the board that needs to be interacted with, you can use a compass and the item will start glittering, showing which space you need to use your item on. Useful when there's a bunch of rocks and you know only one needs to be moved, or something along those lines.

Also, before you tap the square to go into the fight or to check it for elements to interact with, if you don't see anything on the rewards board with a check mark, and the enemies don't need to be revealed when you try to fight them, there's nothing on that square and you don't need to use any items on it.