A simple smart contract with Solidity.

inbox.sol

pragma solidity ^0.4.17;

contract Inbox{
    string public message;
    
    function Inbox(string initialMessage) public {
        message = initialMessage;
    }
    
    function setMessage(string newMessage) public {
        message = newMessage;
    }
    
    function getMessage() public view returns(string) {
        return message;
    }
}