How to make web [alchemy] simple transfer USDT from one external address to the another

Question

I am begginer in crypto staff. I found alchemy from official eth site. I success deploy my simple contract, nft contract.

Now i need to implement transactions with USDT token. I am not sure there is 3 different types ERC TRC and another one. I guest i need ERC20 token.

I found some answers but i cant get it. Looks like complicated situation. I need to deploy MYCONTRACT who looks like :

pragma solidity ^0.8;

interface IERC20 {
    function transfer(address _to, uint256 _value) external returns (bool);
    // don't need to define other functions, only using `transfer()` in this case
}

contract INTERCONNECT_USDT {
    // Do not use in production
    // This function can be executed by anyone
    function sendUSDT(address _to, uint256 _amount) external {
         // This is the mainnet USDT contract address
         // Using on other networks (rinkeby, local, ...) would fail
         //  - there's no contract on this address on other networks
        IERC20 usdt = IERC20(address(0xdAC17F958D2ee523a2206206994597C13D831ec7));

        // transfers USDT that belong to your contract to the specified address
        usdt.transfer(_to, _amount);
    }
}

From : How to receive and send USDT in a smart contract?

What means ?

    // Do not use in production
    // This function can be executed by anyone

If i cant use it on prodc what can i do ?

From alchemy :

Everything you need to know for using Alchemy Notify in your decentralized Ethereum app. Get notifications for external, internal, and token transfers, mined and dropped transactions, and gas price.

This is internal ? If is it then must be external also.

Is it possible to make simple (external) transaction without deploying custom contract?

Because i just wanna simple buy button.

I already use alchemy getBalance , read and write from simple myContract also mint my custom nft tokens etc.

I use metamask chrome ext. for account login.

I am not sure is it USDT still part of ETH network? Because i catch then my get meta data script not work on

Any suggest with some explanation because i still very confussed ;)