The nature of Yom Kippur
Yom Kippur has one positive and two negative commandments associated with it. The positive mitzva is to rest from work and the negative mitzvos are not to do creative work and not eat and drink on Yom Kippur. Chazal extended the prohibitions to not washing, cohabiting, anointing and wearing leather shoes. Unlike other public fasts nowadays that start from the beginning of the day, the fast of Yom Kippur starts from the night before.
The reason for the mitzva
It is a day of atonement and therefore we must do our part to warrant forgiveness. …See Living with Torah – Yom Kippur for a much more in depth understanding to this great and special day.
How to live with this mitzva
Throughout the day, when one feels uncomfortable due to the prohibitions of the day, one should remember that he is doing this mitzva to carry out the will of Hashem and subdue his personal desires to the will of His Creator. He should feel happy and privileged to be commanded to do this as this brings him much closer to Hashem. We are meant to raise ourselves to the levels of Malochim (seen in the lack of physical basic requirements and the reciting of Boruch Shem aloud) and similarly feel like Angels much more spiritual and closer to Hashem.