What is the need of Virtual to overwrite a method in another class?

Question

I am developing a C# system and I came across an inheritance/polymorphism problem. I searched in Google and in Microsoft references, however, I did not find something to clarify my doubts. I am using an event click in an object NavigatorToolbar to enable a new registration, however, in this click, I wanted you to click and get some information from this base class of mine.

public partial class formToolbar : formDefault
{
    public formToolbar()
    {
        InitializeComponent();
        novo.Enabled = true;
    }
    private void novo_Click(object sender, EventArgs e)
    {
        novoRegistro();
    }
    public virtual void novoRegistro() 
    {

    }
    public void novoRegistro(string t)
    {
        MessageBox.Show(t);
    }
}

This code is where you are receiving the event click, and within the function novoRegistro, will be where I will implement the creation of a new record.

public partial class inssCadastroGui : formToolbar
{
        public inssCadastroGui()
        {
            InitializeComponent();
        }

        public override void novoRegistro()
        {
            string teste = "eu sou um parametro";
            base.novoRegistro(teste);
        }
}

And that code is where it’s passing the value to the function. However, when I take the virtual of the code, it stops working. I would like to do so because it would build the bank/system interaction through procedures, thus, through this click, on each screen I would pass the data dynamically. What is the need of this virtual for the creation of this interaction ?