How does solidity stores dynamic arrays in a ethereum smart contract?

dynamicArray.sol

pragma solidity >=0.4.22 <0.6.0;

contract DynamicArray {
    
    uint256[] store;
    
    function getAssembly(uint256 _idx) external view returns(uint256 _value) {
        bytes32 dir = keccak256(abi.encodePacked(uint256(0))); // stored at slot 0
        assembly{
            _value := sload(add(dir,_idx)) // access to keccak256 of slot 0 plus offset
        }
    }
    
    function get(uint256 key) external view returns(uint256) {
        return store[key];
    }
    function set(uint256 _value) external {
        store.push(_value);
    }
}