VB is such a pointless language to me, but here's how you can read a text file directly. You will need an open file dialog to open files and you will also need to add the System.IO namespace to the top. (ex. using System.IO) This is C#, so convert it OR switch to C#.
Code:
if(openFileDialog1.ShowDialog() == DialogResult.OK)
{
listBox1.Items.Clear(); // This will clear any items that may be inside of your list box
listBox1.Items.AddRange(File.ReadAllLines(openFileDialog1.FileName)) // This will read the file you open and display the items in the list box
listBox1.SelectedIndex = 0; // This will highlight the first item in the list box
}
else
{
// Add anything here if you want
}