What does the ⇒ mean in Context Free Grammer? Also, how do I derive/get the L(CFG) from a CFG?

Question

I'm a bit confused. Does the ⇒ simply denote you going through the CFG step by step ? To use a pretty basic-ish example:

sentence ⇒ subject | predicate
subject ⇒ article | noun
predicate ⇒ verb | direct object
article ⇒ THE | A
noun ⇒ CAT | MAN

And so on and so forth? Is the above an L(CFG)?