"And HaShem spoke to Moshe, saying, Speak to the children of Israel and say to them: When you come to the land which I am giving you, and you reap its harvest, you shall bring to the kohen an omer of the beginning of your reaping. And he shall wave the omer before HaShem so that it will be acceptable for you; the kohen shall wave it on the day after the rest day [after the Seder night]. And on the day of your waving the omer, you shall offer up an unblemished lamb in its first year as a burnt offering to HaShem; Its meal offering shall be two tenths of an ephah of fine flour mixed with oil, a fire offering to HaShem as a spirit of satisfaction. And its libation shall be a quarter of a hin of wine. You shall not eat bread or flour made from parched grain or fresh grain, until this very day, until you bring your G-d's offering. This is an eternal statute throughout your generations in all your dwelling places. And you shall count for yourselves, from the morrow of the rest day from the day you bring the omer as a wave offering seven weeks; they shall be complete. You shall count until the day after the seventh week, namely, the fiftieth day, on which you shall bring a new meal offering to HaShem." (Leviticus 23:9-16)
An omer is a unit of weight, equivalent to approximately 3.5-4 pounds. The Hebrew word for barley, which is the grain being harvested, is se'ora.
On the 16th day of Nisan, the barley to be used in the Omer offering was harvested in a grand public event. Residents of the villages surrounding Jerusalem would all come out to take part in the joyous occasion.
After completing the harvest, the kohanim, (priests), would bring baskets filled with barley to the eastern side iof the inner Temple courtyard. There, the newly ripened grain was beaten, roasted, and sifted in thirteen sieves. A handful of the flour was burned on the altar, and the rest was eaten by the kohanim.
Torah states that the first grain offering must consist of fresh barley kernels roasted in a perforated pan, and then ground into a coarse meal. "You must place olive oil and frankincense on it... " (Leviticus 2:15)
Next, the kohen must "wave the Omer before G-d." (Leviticus 23:11) This was done in front of the northeast corner of the altar, the kohen facing westward.
The final step of the Omer offering involved the kohen scooping out a handful of flour from the meal mixture and placing in on the fire atop the altar. This was followed by the bringing of a single male sheep as a burnt offering. From this point on, grain from the new harvest could be eaten.
After waving the Omer at the northeast corner of the altar, the kohen presented the first grain offering before the southwest corner of the altar. This was standard procedure for nearly all meal-offerings.
Following the conclusion of the Omer offering in the courtyard of the Holy Temple, pilgrims leaving the Temple would find the marketplaces of Jerusalem already overflowing with grain products from the new harvest.