Underneath "How to buy usdt?" sits one idea: the coin is the same, the road it takes is not. USDT TRC20 is the version of USDT issued as a TRC20 token on the TRON blockchain, and it is one of the most common ways to send USDT because fees there are usually low. The same coin also exists as BEP20 on BSC and as ERC20 on Ethereum. Each version has its own fees and rules, and a balance on one network never moves to another by itself.
What is the TRON TRC20 network? TRON is a blockchain with its own coin, TRX, and TRC20 is the token standard under which other coins, USDT included, are issued on it. TRX and TRC20 are different things: one is the native coin, the other is a format. TRON counts fees in resources called energy and bandwidth. An account uses the resources it holds or has been delegated, and when they run short the network burns TRX to cover the gap, so one transfer can cost different amounts from different accounts. TRON addresses usually start with the letter T.
What is the BEP20 network? Strictly, BEP20 is a token standard on BSC rather than a network of its own, though wallets and cashiers list it as one. USDT BEP20 is the version of USDT issued under that standard, and its fees are paid in BNB, the native coin of the chain, usually at low cost. Addresses on BSC start with 0x exactly as Ethereum addresses do, and one address can exist on both chains. The look of an address therefore never shows which network a payment is going to use.
ETH, as gas: the gas the transfer uses times the gas price at that moment, which rises when Ethereum is busy.
In energy and bandwidth, from resources the account holds or has been delegated; when those run short, the network burns TRX to cover the difference.
Its network list for sending and receiving should name TRC20 or TRON explicitly; supporting USDT alone says nothing about the network.
Not reliably. Addresses on BEP20 and ERC20 share the 0x format and may match exactly, so the network is picked from the list and matched on the receiving side.
A small first transfer costs one extra fee but shows that the network matches before the full sum moves.