How to Create a ERC-20 Token?

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract MyToken {
    string public constant name = "MyToken";
    string public constant symbol = "MTK";
    uint8 public constant decimals = 18;
    uint256 public totalSupply = 1000000 * (10 ** uint256(decimals));

    mapping(address => uint256) balances;
    mapping(address => mapping (address => uint256)) allowed;

    event Transfer(address indexed from, address indexed to, uint256 tokens);
    event Approval(address indexed owner, address indexed spender, uint256 tokens);

    constructor() {
        balances[msg.sender] = totalSupply;
    }

    function balanceOf(address tokenOwner) public view returns (uint256 balance) {
        return balances[tokenOwner];
    }

    function transfer(address to, uint256 tokens) public returns (bool success) {
        require(balances[msg.sender] >= tokens);
        balances[msg.sender] -= tokens;
        balances[to] += tokens;
        emit Transfer(msg.sender, to, tokens);
        return true;
    }

    function approve(address spender, uint256 tokens) public returns (bool success) {
        allowed[msg.sender][spender] = tokens;
        emit Approval(msg.sender, spender, tokens);
        return true;
    }

    function transferFrom(address from, address to, uint256 tokens) public returns (bool success) {
        require(tokens <= balances[from]);
        require(tokens <= allowed[from][msg.sender]);
        balances[from] -= tokens;
        balances[to] += tokens;
        allowed[from][msg.sender] -= tokens;
        emit Transfer(from, to, tokens);
        return true;
    }
}