How high do you sell?

Buy low, sell high, but how high? I bought 5 cryptocurrencies via the website http://Bittrex.com. I wrote about that yesterday. I placed selling bids (actually, it is an ASK or asking price) or orders for selling some of those coins when they start to go high. I am selling my coins for ten or more times the buying price. I bought a ten thousand Bit Beans. I place an order to sell about 90% of those coins. I am doing that with my other coins too. After placing the order, when the asking price and the bidding price collides, then my orders will begin to transact, to happen, automatically. I have the option to cancel my orders on their Bittrex website too. I do not know if there are cancellation fees or not. I am still learning and I am new to this. Some of my money is in this website, Steemit, and I will continue to collect Steem Power (SP) like a bond, like a smart contract, long-term. I have money in that other coin exchange website, Bittrex, like I said. I have money in my backpack. I don't have an active bank account any longer. Before, I was with Bank of America but then left and went with the U.S. Bank. Now, no bank. I do have money in a Electrum Bitcoin wallet on my computer. In other words, I have money divided and in a few different places.
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On Bittrex, I see 3 exchange markets, the BTC Bitcoin market, the ETH Ethereum market, and a third like USDT market. What is USDT? Is it the same as the USD centralized Federal Reserve regulated non-American American so-called dollar which is probably not really backed up or backed by gold and stuff as it once was decades or more ago.
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Can you buy BTC from the ETH market?
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I saw ETH in the BTC market but did not see BTC in the ETH market.
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Which websites do you use to trade / buy / sell / exchange and why?
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What other ways can people buy and sell and everything?
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What other advice can you give me and people?
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What happened to Poloniex and can I get my money back from them? Did they steal it?
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I am still learning and will continue to share my experience each day or week.
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Here is some information and photos of what I am selling.
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