How to refute kings gambit as black

Play g5 or d5 instead of Nc6.

Falkbeer countergambit like @TalMagicalDragon said

www.chessgames.com/perl/chessgame?gid=1075588

this is the line Danya Naroditsky recomends
1.e4 e5 2.f4 exf4 3.Nf3 d5 4.exd5 Nf6
if white deviates from those moves they are already in trouble, but take a looke with the engine yourself

but if you want to continue with your d6 line, you probably have to play g5 at some point so they can't take the pawn back and get their ideal setup
in the game you just let him get everything he could dream of

You can't refute the King's gambit

Nf6 is well within my preparation and most of your opponents will know more poisons than you #13 oh i see you mean nf6 after d5 i taught its nf6 after nf3

can you please show the variation where kings gambit is refuted @TheKingClash

Or what those right moves are .

@kitpuff
By not accepting it! (logic)

Well, on a serious note, play the Falkbeer (d5) or the Classical Defense (Bc5).
For more choices in them, consult:
en.m.wikipedia.org/wiki/King%27s_Gambit