It was a place where the high priest would go in, once a year, on the Day of Atonement, to sprinkle the blood of an animal upon the Ark of the Covenant and the mercy seat which sat on top of the ark. The animal was sacrificed on the Brazen Altar and the blood was carried into the most holy place. The golden censors were also found in the most holy place.
It is said to be the place where the presence of God dwelt. In the wilderness, on the day that the tabernacle was first raised up, the cloud of the Lord covered the tabernacle. There are other times that this was recorded, and instructions were given that the Lord would appear in the cloud upon the mercy seat, and at that time the priests should not enter into the tabernacle (Leviticus 16:2).
The Tabernacle in the Wilderness