The song references Celebrimbor (as the Bright Master), Talion (as the Ranger), as well as the One Ring (as the "precious"), and Bilbo Baggins. It also shows Gollum's plan: only aiding Celebrimbor in order to have him lead him to the One Ring and then steal it from him.
Bright Master will takes us to the precious, we shows him.
We shows him and he rewards us.
We likes the Bright Master, the royal one. Smells sweet, like flopping fishes.
But filthy tricksy Ranger comes along. Cruddy Ranger, smelly, stinky Ranger.
He hurts us. He steals from us... like Bagginses... Bagginses...
He'll shows us, then we'll takes it.
He'll shows us the he'll steals it. No! No!
We'll takes it from him... we'll takes it from... oh sharpest of sharpsies.
But not hurting! No hurting! Gentle sharpsies! Shows us, Bright Master.