i also have another question, if i want invest ethereum here, how to do it, i heard other people saying its not good to send from exchange

sorry i didnt explain very well, i mean if i send from polo account, i heard that its not good to send from there, because its hotwallet or something like that
can somebody please explain why its not good, and how to invest them safely?

No dont send from exchange, the reason is because you wont get back to the address you sent from.The poloniex withdraw account is not the same as your deposit account.
What you need to do is create an online walet, and send your ether there, and from there you have to deposit:
Try:
http://www.myetherwallet.com/or
https://www.ethereumwallet.com/index.htmlIts pretty easy to use, just always invest from your own controlled wallet, never an exchange. Good luck!
so if i invest form the myetherwallet it will work right? and the profit willbe sended back to the address i send from?