What does the phrase "GG NOOB" mean?

I have just recently started to use this new thing called the "internet", so I may be a little unfamiliar.

I am new to games and I see people say GG NOOB or AHHAHAHAHAHA GG NOOBLET. Im wondered what it meant, is it an insult? Exclamation? I tried saying "God Bless You" then they say "WTFFF JESUS FREAK". Like really, how ignorant are these poor people? There is a special place in hell for such people who disrespect our glorious God.

Along with Athiests.