At the time of the temple, the Mitzvah of counting the Omer was commanded by the Torah, today due to our sins, it has become a commandment of our sages.

Consequently in the text “Leshem yichud” that we say before saying the Omer, one will not say “I am coming to fulfill the positive commandment of counting the Omer” one will say “I am coming to fulfill the commandment of counting the Omer”.

The time of counting (Sefirah): according to the strict law, one counts at sunset, primarily the ideal time to count when 3 stars appear .if one forgets to count at night one will then count the next day without a blessing.

Counting in the morning: it is a worthy custom to count the Omer every morning after the prayers, without a blessing so that if one forgot to count the previous night and then counts during the day, he may then continue to count the Omer with the blessings the following night.

Giving merit to many people: A nice custom exists in many communities during the Omer, between Mincha and Maariv (prayers of the afternoon and of the evening): one reads the Pirkei Avot and one listens to a Torah lecture from a Rabbi until the stars come out, then one says Maariv and counts the Omer.
Perhaps through this merit, the community will then want to continue all year round, as one Mitzvah generates another.
Any person who persuades his fellow brother to accumulate merits is guaranteed that no sin will come about through him.

The correct way to say the Omer is as follows:
First, the chazzan (public representative) or the rabbi of the community say the blessings and counts the Omer, then the public will do so.
It is preferable to do it in this way, to prevent mistakes when counting.

If a congregation finishes to pray before twilight, and the chazzan knows that if he doesn’t count right away some members will forget to count, it will be a Mitzvah for him to count right away without waiting for the stars to come out.

Error in the counting: if one forges to count in the night and the next day, one may not continue counting the Omer with the blessings.
One should then ask somebody else to have him in mind whilst he makes the blessings, and then one may count, if one has a doubt if he counted or not, one may continue to count with the blessings.

One who counts with no blessings one day (even unintentionally) has accomplished the Mitzvah, therefore he may not repeat the Omer again with the blessings that evening.    
Consequently, if one is asked: ”what day of the Omer are we today?”
the  answer should not be “today we are this day..” (Since it will be considered as if we have already counted) the answer should, therefore, be: “yesterday it was …”

By doing so one will, therefore, understand what to count that day.

If accidentally one did answer that question: “today is …” that evening one will not say the blessings, however, if one did not mention the word “today” one may count that evening with the blessings.

Training of Mitzvot: it’s a Mitzvah to educate young children to count the Omer with the blessings and even if they forget one day, they may continue saying the Omer with the blessings.

Ladies are exempt from the Mitzvah of counting the Omer if they wish they may count without the blessings.