To convert string to binary in c#, you can drag the textbox, label and button from your visual studio toolbox to your winform, then layout your UI as shown below.

Next, Create the StringToBinary method allow you to convert text to binary as the following c# code.
public string StringToBinary(string data)
{
StringBuilder sb = new StringBuilder();
foreach (char c in data.ToCharArray())
sb.Append(Convert.ToString(c, 2).PadLeft(8, '0'));
return sb.ToString();
}
Finally, Add code to handle the Convert button click event.
private void btnConvert_Click(object sender, EventArgs e)
{
txtOutput.Text = StringToBinary(txtInput.Text);
}
Press F5 to build and run your project, then you can enter a string and convert to binary sequence in c#.