most times, the beginning of a beracha is Baruch Atah Adonai, etc. which is usually translated as Blessed are You God, etc.
what does it mean to say that God is blessed? (on the surface it implies someone blessed Him therefore He is blessed.)
Pathways to Prayer understands ברוך (Baruch) to be an adjective similar to רחום (Rachum - source of mercy), meaning that HaShem is the source of all blessing.
Rabbi Yosef Albo, in Sefer Ha-Iqqarim / The Book of Roots, ma'amar sheini, perek 26, elaborates a definition:
ברוך שם משותף, יאמר על מקבל הטוב והשפע מזולתו...ויאמר על נותן הטוב והשפע לזולתו...וזה כי ברכה שם נאמר על ריבוי ותוספת טוב ושפע, וכשיאמר על המקבל ברוך פָּעוּל....וכשיאמר על הנותן יהיה ברוך שם התואר
Barukh is an amphibolous term, used [both] for one receiving good and influx from another...and for one giving good and influx to another....and this is because brakhah is a term denoting increase and addition of goodness and influx, and when it is used for the receiver, [the form of the word is to be construed as] a passive....and when it is used for the giver, [it is to be construed as] an adjective.
In Nefesh Hachaim Sha'ar 2:2, Rav Chaim Volozhin understands blessing to be a request for abundance. He explains that by saying Baruch Atah Hashem, we are effectively requesting for God to manifest himself with greater abundance in this world. I am not a kabbalist, and do not truly understand what this means, but there you go.
The word ברוך is related to the word בריכה, which means a spring. A spring is a source of water which (from our perspective) is increasing its flow without drawing on any previous source. Baruch Ata means "You are the source" - Hashem is the ultimate Source of all existence, and it is the "flow" of "energy" which He infuses into Creation which sustains and maintains it.
You the extraordinary in the ordinary the Wellspring of goodness