From the FAQ:
In order to display an interactive board within a forum post you will need to enter the following code when writing your post:
[pgn ]Your PGN Here[/pgn ] {leave out the space which appears here in each set of brackets, to make it work}
As an example, to view the Immortal Game, you would post this :
[Event "Immortal game"] [Site "London"] [Date "1851.??.??"] [Round "?"] [White "Anderssen,A"] [Black "Kieseritzky,L"] [Result "1-0"] 1.e4 e5 2.f4 exf4 3.Bc4 Qh4+ 4.Kf1 b5 5.Bxb5 Nf6 6.Nf3 Qh6 7.d3 Nh5 8.Nh4 Qg5 9.Nf5 c6 10.g4 Nf6 11.Rg1 cxb5 12.h4 Qg6 13.h5 Qg5 14.Qf3 Ng8 15.Bxf4 Qf6 16.Nc3 Bc5 17.Nd5 Qxb2 18.Bd6 Qxa1+ 19.Ke2 Bxg1 20.e5 Na6 21.Nxg7+ Kd8 22.Qf6+ Nxf6 23.Be7+ 1-0
Use "reply and quote" from this post, to see exactly what was done, and replace the PGN with your own. You will get the pink error message if the material between the two bracket sets is not a valid PGN.