One apple daily, is it good?

Yes, of course!: But it won't keep the doctor away. However, the more fruits & vegetables that you eat each day, the better off you'll be. Many many studies have linked greater consumption of fruits & veggies to lower all-cause mortality. And don't forget to exercise regularly. That helps, too.

Yes: Apples provide dietary fiber and many important nutrients that support good health. This along with a balanced diet can be beneficial.