What is it about? On this day Israel would make a sacrifice unto the Most High to atone for their sins. Israel would make offerings of rams and bullocks and lambs without blemish to be accepted before the Most High.
How do we celebrate it? We are to have a Holy Convocation in which we do no servile work and afflict our souls with fasting and prayer. A guide to how to fast is shown in these scripture: (Isaiah 58:1-14 and Matthew 6:16-18)
How Christ fulfilled this Holy Day: After being crucified, Christ went into the heavenly tabernacle in order to shed his blood for the nation of Israel. Due to this, we no longer are required to make sacrifice on this Holy day.
Leviticus 23:26-32, Numbers 29:7-11, Isaiah 58, Mat.6:16-18, 2Cor. 7:10, Lev. 16:29-31, Psa. 35:13 , Psa. 69:10-11, Isa. 58:3-7, Lev. 16:1-2 ,Lev. 16:3-6, Lev. 16:11, Heb. 9:7, Lev. 16:17;24, Heb. 9:7,