Yes apples do have seeds BUT they contain cyanide. You're very unlikely to eat enough apple seeds to poison yourself, so don't worry too much if you swallow one on the odd occasion. Swallowing whole seeds won't cause harm because they have a coating which protects them from digestive enzymes, causing them to pass through your digestive system undamaged. But chewing and swallowing a large number of apple seeds a one sitting could be dangerous.
Apple juice and smoothies often contain whole crushed apples, including the core and seeds. Because the apple seeds get crushed during the juicing process, they could release some cyanide, so it's definitely advised to core the apple before juicing it.
Here are two easy ways to core an apple:
• Use an apple corer: Push it through your apple, twist it, then lift it back out to remove its center.
• Use a paring knife: Cut the apple into quarters or halves, making sure not to cut into the cores, discard the cores.