The Torah writes: "And you shall count for yourselves from the morrow of the Shabbat, from the day that you bring the omer [offering] that is raised, seven complete weeks there shall be until the morrow of the seventh week you shall count fifty days" (Leviticus 23:1516).
The Omer is counted from the second night of Passover through the night before Shavuot. It is best to count the Omer at nightfall, immediately after the evening prayer. However, one may count at any time throughout the night.
In remembrance of the tragic death of 24,000 disciples of Rabbi Akiva, several mourning practices are observed during the weeks between Passover and Shavuot.
We count the days between Pesach and Shavuot as we prepare to receive the Torah again on the Festival of Shavuot. This is called “Counting the Days of the Omer,” or “Sefirat Ha’Omer.” Here’s how to do it.