The first thing to be placed within the tabernacle was the ark of the testimony, as containing the foundation of the covenant between God and Israel, and being the special token of God's presence with his people.
See the comment on Exodus 25:10. The "two tables" were placed within the ark before it was brought into the tabernacle (Exodus 25:20, Exodus 25:21). Cover the ark with the veil—i.e; "hang up the veil in front of the ark, so as to cover or conceal it."