To run scripts, you will need to create a folder called Scripts (or scripts) inside your game folder.
You can read about this in the included guide.
It is in the subfolder of this app called Tutor/Guides:


            

using GTA;
using GTA.Native;
using System;
using System.Windows.Forms;

namespace YourNameSpace
{
    public class Basic : Script
    {      
        public Basic()
        {
            Tick += OnTick;
            KeyDown += OnKeyDown;
            KeyUp += OnKeyUp;
        }

        private void OnTick(object sender, EventArgs e)
        {
           // code goes here
        }

        private void OnKeyUp(object sender, KeyEventArgs e)
        {
            if (e.KeyCode == Keys.T)
            {
               // code goes here
            }
        }

        private void OnKeyDown(object sender, KeyEventArgs e)
        {
            if (e.KeyCode == Keys.Z)
            {
               // code goes here
            }
        }
    }
}

             

       
using GTA;
using System.Windows.Forms;

namespace YourNameSpace
{
    public class Basic : Script
    {      
        public Basic()
        {
            KeyDown += OnKeyDown;
        }

        private void OnKeyDown(object sender, KeyEventArgs e)
        {
            if (e.KeyCode == Keys.Z)
            {
                GTA.UI.Screen.ShowSubtitle("Hello World", 2500);
            }
        }            
    }
}
      
            

Required Installations - Links
Script Hook V
ScriptHookVDotNet


Excellent Resources - Links
Visual Studio - Free Community Version
GTA V Toolkit - How to Install and Fix Mods
Original Menyoo Trainer
            

If you want to have your compiled script, as a .dll file, go directly into your GTA V Scripts folder:
1. From Visual Studio Menu (very top) select Project
2. Select the last option which will be your ProjectName, Properties.
3. Click on Build Events
4. Go to the lower box entitled Post-build event command line
5. Enter this line, adjusting for your path:
COPY "$(TargetPath)" "P:\SteamLibrary\steamapps\common\Grand Theft Auto V\Scripts"


This will place your script in the folder above, ready for gameplay.