To bless means to give a gift. In verbally blessing another you are connecting him to the power of God. To bless a person is to use your Christian authority in Jesus' name (that is to say, you are under Jesus' authority and, so, you are authorized to use his authority) and direct the grace of God to him. You can bless a congregation, even an inanimate object like a building or an abstraction like your job.
Bless those who persecute you; bless and do not curse them. (Romans 12:14 ESV)
And when Peter saw it he addressed the people: "Men of Israel, why do you wonder at this, or why do you stare at us, as though by our own power or piety we have made him walk? And his name--by faith in his name--has made this man strong whom you see and know, and the faith that is through Jesus has given the man this perfect health in the presence of you all. (Acts 3:12,16 ESV)The late Church of God minister, Maurice Berquist (1923—1993), wrote a fascinating book entitled The Miracle and Power of Blessing. You can read it online for free by going to this link. You don't have to agree with all of the points, illustrations or conclusions of Berk to, well, be blessed by the book.
I bless you in the name of Jesus in order that you might bless others.
I'd love to build up a great church based on blessing! Love! Joy! Peace! The presence of the Holy Spirit! Salvation! Sanctification! Healing! Blessing!