The difference between a coin and a token is not value but structure. A coin is inseparable from its network: it is born there and serves as payment for transfers. A token is a record on someone else's network, made by that network's rules.
Why this matters when you exchange
Because of the fee. When you send USDT, and USDT is a token, you pay not in USDT but in the coin of the network that issued it: TRX on TRON, ETH on Ethereum, BNB on BNB Smart Chain. A wallet with a full USDT balance and an empty network coin balance cannot send a transfer.
And because of identical names. The very same USDT exists as a token on several networks at once. The name matches, the networks differ, and a direct transfer between them is impossible.
What it costs to issue a token
Almost nothing: a few dollars in fees and half an hour of time. That is why there are tens of thousands of tokens, and the vast majority are worth nothing. The mere existence of a token says nothing about the company behind it or its obligations.
How to tell a real token from a fake
Every token has a contract address, the only exact identifier. Names and logos are copied freely: dozens of «USDT» tokens exist on-chain, and only one of them is real.
Take the contract address from the issuer's site or from a reference source such as a block explorer, not from a chat message. A wallet that has added a token by the wrong address will show a nice balance that cannot be sold.