The Ben Ish Hai says one should eat the day before Kippur the amount of two days worth of meals.
On Yom Kippur, of course we do not eat.
Starting from Candle lighting before nightfall until 3 stars are seen the next day we fast.
The day of atonement is a day for repentance. Several things we do are to refrain from:
Eating or drinking
Wearing Leather Shoes
Applying oils or lotions
The reason why we fast is to focus on repentance and self- improvement. To introspect on what we can do better and what we must refrain from in the new year.
Yom Kippur our evil inclination is taken away for only this one day a year to allow us to become closer to the creator. The fasting is an opportunity to become angel-like and be able to remove all external influences to connect and create a deeper relationship with G-d, that we hope will continue the rest of the year.
Gmar Hatima Tova / A Good Finishing Seal for You and your Family.