Apples are reoccurring items in The Legend of Zelda series.
A Link to the Past
In Twilight Princess, apples are sold along with Bread and Pretty Flowers at one of the shops in the Hyrule Castle Town market. The 'get item' chime will play, but Link is not able to pick up the apple, nor does it have any use.
A Link Between Worlds
If Link dashes into a tree or uses the Tornado Rod next to it, apples might fall out. Each red apple that Link acquires restores one heart. Red apples are fairly common and easy to find. Green Apples are much rarer, and will restore three hearts. Link's chances at finding them are better when the StreetPass Tree is planted by Gramps. This apple tree has more apples if Link gets more StreetPasses. It is the only tree that has visible apples. Apples can also be caught with the Net and stored in a Bottle for later consumption.
Breath of the Wild
"A common fruit found on trees all around Hyrule. Eat it fresh, or cook it to increase its effect."
Apples (162 in the Hyrule Compendium) can be found all over the place in Hyrule, typically hanging from trees, but also in Wooden Crates located around Bokoblin Camps and can spawn from Amiibo. One apple will restore ½ of a heart. Apples can also be used as an ingredient for Red Dye at the Kochi Dye Shop. Apples can be cooked on a fire to obtain a Baked Apple, which will restore ¾ of a heart. They can also be used in a variety of Recipes, but offer no special cooking effects.