Why do we “count the Omer”?
We are commanded to count seven weeks from the time that the omer, the new barley offering, was brought in the Beit HaMikdash. We begin counting on the sixteenth of Nissan, the second night of Passover, and continue until Shavuot, which is the fiftieth day after the offering.
When do we count?
We count in the evening after the stars come out. If one forgot to count, s/he may count during the entire day without a blessing and continue to count with a blessing the following evening. If one forgot to count a particular day completely, s/he may continue to count the following days but without a blessing.
How do we count?
We recite the blessing: “Blessed are You, Lord our God, King of the Universe, who has sanctified us with His commandments, and commanded us concerning the counting of the Omer.”, and then recite the text for the particular day’s count.