Berachot are the Jewish way of saying thank you to the Source of all. From when we open our eyes in the morning to when we close them at night, on every drop of water we drink, on fragrant smells, rainbows as well as on most mitzvot we do. In an average day an observant Jew will say around 100.
There are three types of berachot. The first are blessings of enjoyment: before and after food or drink or on smelling something lovely. The rabbis say that do take enjoyment from this world without saying a berachah is tantamount to stealing from God (Talmud Berachot 36a). The second type is on mitzvot, eg before putting on tefillin, sitting in a succah or putting on a mezuzah.
The third group are blessings of thanksgiving, usually for experiencing something remarkable; eg on hearing thunder, seeing lightning, or seeing a great thinker or sage or a powerful ruler. (I once got to say the last of these when an American president zoomed past our the end of our street in Jerusalem, clearly visible in the middle of a forty-vehicle motorcade.)