what's a png file?

It's a file that holds the information of a chess game or series of games. It allows you to replay the game yourself or open the game with various chess software.

Pgn stands for "portable game notation." See wiki for all the details and rules. For most of our purposes, it's  a somewhat universal way of notating a chess game in a way that computers can interpret them.

Here is an example - it's one of Morphy's most famous games against Paulsen.  I grabbed it easily from chessgames.com. You can see how the pgn is constructed with information on top within brackets and quotes [" "] with the algebraic notation following.  This game also contains annotation within the moves. They're surrounded with { }.

[Event "1st Amer. Chess Congress"]
[Site "NYC"]
[Date "1857.??.??"]
[EventDate "?"]
[Round "?"]
[Result "0-1"]
[White "Louis Paulsen"]
[Black "Paul Morphy"]
[ECO "C48"]
[WhiteElo "?"]
[BlackElo "?"]
[PlyCount "56"]

1. e4 e5 2. Nf3 Nc6 3. Nc3 Nf6 4. Bb5 Bc5 5. O-O O-O 6. Nxe5
Re8 7. Nxc6 dxc6 8. Bc4 b5 9. Be2 Nxe4 10. Nxe4 Rxe4 11. Bf3
Re6 12. c3 Qd3 13. b4 Bb6 14. a4 bxa4 15. Qxa4 Bd7 16. Ra2
Rae8 17. Qa6 {Morphy took twelve minutes over his next move,
probably to assure himself that the combination was sound and
that he had a forced win in every variation. -- Chernev} Qxf3
{!!} 18. gxf3 Rg6+ 19. Kh1 Bh3 20. Rd1 {Not 20 Rg1 Rxg1+ 21
Kxg1 Re1+} Bg2+ 21. Kg1 Bxf3+ 22. Kf1 Bg2+ {The "quiet"
22...Rg2! would have won more quickly. Zukertort gives: 23.Qd3
Rxf2+ 24.Kg1 Rg2+ 25.Kh1 Rg1. } 23. Kg1 Bh3+ 24. Kh1 Bxf2
25. Qf1 {Absolutely forced.} Bxf1 26. Rxf1 Re2 27. Ra1 Rh6
28. d4 Be3 0-1

By clicking on the little chessboard in the toolbar above, I am able to paste this pgn notation into the dialogue boxes and present the game as below:

Depending on your chess program, database or game viewer, you may also be able to paste a game into it, although sometime you must save the game and open the file from the application.

thanks didnt realise it was simply chess related...lol i feel like a real idiot...lol

Don't worry - we all had to learn at some point!