wählen means to choose one of them. To stick with the fruits introduced by this answer: If there are 5 apples and 8 oranges, you could choose an apple. No matter which exact one. Just an apple. -- Du wählst einen Apfel. auswählen means you want to pick a particular apple. Not just an apple, but exactly this apple. -- Du wählst diesen bestimmten Apfel aus.