Pls can someone tell me what it is?You can buy something with that?

You can win shiai tokens at events by GMs (Gamemaster).
You can get certain items only with shiai tokens.
Just take a look at the event s at the shiai token thread to see them.

http://forum.toribash.com/showthread.php?t=448147
It is basically a currency, you get them in GM events in-game and on the forums(and sometimes non-gm events), but is not tradable/sellable/marketable. The only way to get rid of them is by using them to buy a ST item, which can be done by messaging any GM to exchange them(the prices and the items are in the thread) or atleast that's what I know so far.

Thank you very much.