So while on bittrex i trade my crypto to USDT and keep them in the exchange while I buy again? It's like a crypto US dollar correct?
Yes, but recently Tether (USDT) has been swinging a few cents either way. It's not necessarily exactly $1.
https://coinmarketcap.com/assets/tether/it is worth reminding that "a few cents" while the price is small is A LOT OF change.
for example you may see $0.95 is only 5 cents but when you have for example 2 bitcoins in USDT that is $5000 @$2500 but it is 4750 USDT meanign $250 loss.