In Israel and most Sephardi communities outside Israel, the Cohanim, priests, bless the people after the morning service every day. The blessing (“May the Lord bless you and keep you”) is taken from Numbers 6:22-27. Although the mitzvah is ideally to be performed by Cohanim in the Temple, the same mitzvah (with minor variations) is in force today as well. Rambam lists this mitzvah as one of the 60 which remain obligatory in all times under normal conditions.
Apart from bar- and batmitzvah celebrations and weddings, Ashkenazi Jews outside Israel only give the priestly blessing during services on festivals. This is based on the opinion that the blessing must be given with joy and, during the long exile, the festivals were the only times when people felt reliably joyful.
The priests put their tallitot over their heads, raise their hands, separating their fingers in groups of two, turn to the community and say the blessing. The finger separation pattern was made famous by Mister Spock in Star Trek, who iadopted a one-handed version as the Vulcan Salute.