Please do not come and share something you know nothing or little about. I was also excited when I saw the title. I was a little bit disappointed. You can make inquiries to know about a particular site or app.
There is no way stormgain will allow you to withdraw your mind USDT into your wallet. You can only use your mined coins to trade Crypto pairs and metals. I think they have commodities now. And the value is not stable cos it is measured in the value of bitcoin. So if Bitcoin should drop, your mined coins value drop with it.
The minimum amount for trading is $10 and if it is lower by a cent, it will not be placed.