Fullmetal Alchemist: Brotherhood is a retelling of the story based off the manga, and is not directly related to the first Fullmetal Alchemist series.
Edward and Alphonse Elric are two brothers living in a world where the practice of alchemy flourishes. After their mother passes away, the brothers work together to try and bring her back using alchemy, but without success. Their failure results in Edward losing his left leg and right arm, while Alphonse loses his entire body and has his soul attached to a suit of armor. Years later, they join the military for the opportunity to locate the Philosopher's Stone; the one thing that is capable of restoring their bodies.
This guide covers the English version. For the Japanese version, go to: Hagane no Renkinjutsushi: Fullmetal Alchemist
(01-14) -- "again" by YUI
(15-26) -- "Hologram" by NICO Touches the Walls
(27-38) -- "Golden Time Lover" by Sukima Switch
(39-??) -- "Period" by Chemistry
(01-14) -- "Lie" by SID
(15-26) -- "LET IT OUT" by Miho Fukuhara
(27-38) -- "Tied Hands" by Lil'B
(39-??) -- "Shunkan Sentimental" by SCANDAL