Between the festivals of Pesach and Shavuot Jewish people count the Omer. The first night of the Omer falls on the second night of Pesach and the last night of the Omer falls on the night before Shavuot. The best time to count the Omer is immediately after the evening prayer (known as Aravit or Maariv) but one can count the Omer at any time throughout the night.
After sunset one should avoid saying what day of the Omer it is before reciting the blessing. This means that if someone asks you what day of the Omer are we counting today you should respond with “yesterday we counted x days.” If you do answer with just the number, i.e. “22” then you may still count the Omer with a blessing.
The counting of the Omer, as we have already stated, takes place at night. If one forgets to count the Omer at night one may count during the day without the blessing and then continue to count on subsequent nights with a blessing. However, if one forgets to count at night and in the following day, one must count the rest of the Omer without a blessing too. In the case of someone who is in doubt as to whether he counted the previous night and did not count during the day, he may continue counting with a blessing. If one is within the half hour before twilight, one should not count eat until one has counted the Omer.
If one is in Synagogue for evening prayers, the cantor recites the blessing out loud and counts the Omer after which so does the congregation. This is all done while standing. The blessing over the Omer is as follows,
“Blessed are you, L-rd our G-d, King of the Universe, who has sanctified us with His commandments and commanded us concerning the counting of the Omer.”
Every night of the Omer the Omer is counted according to the number of days followed by a summary of the weeks and days that have passed up until now. For example, on the twenty-third day one would say, “Today is twenty-three days, which is three weeks and two days of the Omer.”
After counting the number of days, a short prayer is recited beseeching G-d to allow us to once again serve Him in the Temple. After this, a psalm is recited, as well as a powerful Kabbalistic prayer called Ana B’Koach and a final prayer that refers to the unique Kabbalistic characteristics of the same day, asking G-d to help us refine these characteristics in ourselves.