Introduction

Creating a smart contract via smart contract has many advantages and use cases over manually creating and deploying smart contracts. 

Deployer SC code

Smart Contract A

Contract to be deployed will be a simple storage smart contract as follows

contract Storage {

    uint256 number;
    event stored(uint256 _value);

    function store(uint256 num) public {
        number = num;
        emit stored(number);
    }
}

Deployer Smart Contract

We will create one variable of type Storage, which is our contract to be deployed, to store created contract's instance.  

contract Deployer {

    Storage a;

    function deploy_sc() public {
        a = new Storage();
    }
    function get_sc() public view returns(Storage){
        return a;
    }
}

Here we need to deploy Deployer smart contract and call deploy_sc method.

Complete Code

// SPDX-License-Identifier: GPL-3.0
pragma solidity ^0.8.0;

contract Storage {

    uint256 number;
    event stored(uint256 _value);

    function store(uint256 num) public {
        number = num;
        emit stored(number);
    }
}

contract Deployer {

    Storage a;

    function deploy_sc() public {
        a = new Storage();
    }
    function get_sc() public view returns(Storage){
        return a;
    }
}