A USDT wallet is any wallet that supports USDT on the network being used, because USDT runs on several networks, among them TRC20 on TRON, ERC20 on Ethereum and BEP20 on BNB Smart Chain. A balance on one network does not move to another by itself. To create a USDT wallet, set up the app as usual, back up the words, then add USDT and choose the network before copying the address. Fees are paid in that network's coin: TRX on TRON, through energy and bandwidth or TRX burnt for them, ETH gas on Ethereum, BNB on the BNB chain.
Creating a bitcoin wallet takes a few minutes in most apps. The app generates fresh keys, shows a short list of backup words to copy onto paper, and then displays a receiving address. How to create a bitcoin wallet safely comes down to that backup step, because without it a broken phone takes the coins with it. A bitcoin account is something else: a login at an exchange that holds keys for its users. Anyone who wants to open a bitcoin account there usually faces identity checks, while owning bitcoin in a personal wallet needs no account at all.
A bitcoin wallet on a phone suits small, frequent transfers, since the camera can scan the address code a casino cashier shows. The phone is also the weak point: it can be lost, stolen or infected, so a screen lock, current updates and a modest balance keep the risk within reason. A bitcoin wallet app belongs on the device only from the official store or the developer's own site, checked by the developer's name. Fake copies borrow known names and icons, and no app stays safe once its backup words have been typed anywhere else.