Can anyone explain me what is this ? sorry for a noob question.
No problem, everybody needs to learn...
I think the bitcoin site gives a better explanation than i'll ever will:
https://en.bitcoin.it/wiki/TestnetThe TL;DR (and newbie friendly) version:
Testnet is basically a complete blockchain that runs next to the bitcoin blockchain. The coins on the testnet are worthless, and can be used to test out procedures and codes without risking losing real bitcoins. It's basically a newbie and developer sandbox in which you can play
