Bitcoin can gain or lose ten percent in a day. That is awkward for payments: the seller does not know what they will actually receive. Stablecoins solve exactly this problem, carrying a familiar unit of account onto the blockchain.
What backs the peg
For large stablecoins, the issuer's reserves: the company promises to exchange the coin for a dollar and holds cash and short-term instruments against it. The rate rests on that promise, not on network mathematics.
It follows that a stablecoin is not the same thing as a dollar in a bank. The risk here is not price movement but the issuer itself: if it cannot keep the promise, the peg stops holding.
What people choose in practice
USDT is the most widespread and therefore the most liquid: it is accepted almost everywhere. USDC is considered stricter on reporting. For exchanging into hryvnia there is usually no difference; for long-term holding the choice is meaningful.
Why the rate still drifts a little
One USDT is worth not exactly a dollar but around a dollar: 0.999 or 1.001. That is normal, because the market sets the price and the issuer's promise only keeps it near parity. Noticeable deviations happen in moments of panic, when everyone wants out at once.
One name, different networks
USDT exists on TRON, Ethereum, BNB Smart Chain and several other networks at the same time. It is the same token in substance, but not in address: you cannot move it directly from one network to another, you need an exchange service or a trading platform.
That is why an exchange always specifies not just «USDT» but «USDT TRC20» or «USDT ERC20». A line with no network stated is a reason to ask, not to guess.
Read more: Where to start and what not to do