The portable Sanctuary built by the Children ofin the Sinai Desert--known as the or the " "--was inaugurated on the first day of the Hebrew month of of the year 2449 from creation (1312 BCE). Beginning on that day and continuing through the first twelve days of Nissan, each of the tribal leaders--the " "--of the twelve tribes of Israel brought inaugural offerings as the representative of his tribe.
It is our custom to commemorate the Mishkan's inauguration each year by reading, on each of these twelve days, the verses from thewhich describe the offerings of that day's . These verses are traditionally read after the morning prayers, but can be recited anytime throughout the day.
The reading is followed by a brief prayer, in which we say, "May it be Your will,my G‑d and G‑d of my fathers... that if I, Your servant, am from the tribe of ______ whose section of the Nasi I have read today in Your Torah, may all the holy sparks and holy illuminations that are included within the holiness of this tribe shine upon me, to grant me understanding and intelligence in Your Torah and my awe of You, to do Your will all the days of my life...."
On the thirteenth of Nissan, we read the totals of all the sacrifices, and then read about the kindling of the Tabernacle's-- the contribution of the priestly tribe of (which was not counted among the 12 tribes). The "May it be Your will..." prayer is not recited on this day.