Create a new VB project.

Go to Toolbox -> "Dialogs" and double click "OpenFileDialog"

Double click the blue header of your window form and go to the sub of this form.

Add this code inside the sub:
OpenFileDialog1.ShowDialog()

OpenFileDialog1 - is the name of the function we have added to our program. This option is used for choosing a file on your hard drive. You can change the (Name) value of this in the design tab -> Properties.
.ShowDialog() - allows you to see the selection screen of the "OpenFileDialog" option

Code:

Public Class Form1

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
OpenFileDialog1.ShowDialog()
End Sub

End Class

When the window form loads -> you'll be able to choose a file from your hard drive. You can change the event of the form: "MyBase.Load"  to   "MyBase.Click"  so you will have to click first on the form.

In the design page, go to Toolbox -> "Common Controls" and drag a Button to your form.
Double click the button and go to the sub section. The default event for a button is obviously: Click.

Cut out the "OpenFileDialog1.ShowDialog()" from the form sub and paste it into the button sub. Erase what's left of the form sub.

The new code:

Public Class Form1

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        OpenFileDialog1.ShowDialog()
    End Sub

End Class

Start the program. Click on the button to load a file.
It makes more logical sense to have a button doing this then the form itself. It's what the users of the program would expect.

When the loading option is started, you might have noticed that it says:
File Name: OpenFileDialog1
before choosing the "open" or "cancel" options.
This can be changed. Go to design page -> click on the "OpenFileDialog1" option -> go to properties window -> Find the "FileName" value. Change as you prefer, you can also erase all.
 
Now we can combine the code from tutorial 01 and load the data from a chosen .txt file.

First add a textbox element to your form and put the button right bellow it. Choose multiline for the texbox.
Add: Imports System.IO to the program.
Add: Private a1 As Streamreader

We will not have a pre-determined Streamreader path for "a1" cause we will be choosing one.

Right below "OpenFileDialog1.ShowDialog()" we will add:

- File.OpenText - function used for dealing with files. We have chosen to open the text of a file
- OpenFileDialog1.FileName - after we have chosen (loaded) a file, "OpenFileDialog1" will store many of it's values. "Filename" is the address of the file on our hard drive.
- File.OpenText(OpenFileDialog1.FileName) - basically says: "we will open the text of a file - the file path of that file is going to be the one (previously) chosen in "OpenFileDialog1""
 - a1 is able to store a whole text because it's declared as a StreamReader

Current Code:

Imports System.IO

Public Class Form1

    Private a1 As StreamReader

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        OpenFileDialog1.ShowDialog()
        a1 = File.OpenText(OpenFileDialog1.FileName)
        TextBox1.Text = a1.ReadToEnd()
    End Sub

End Class

Start the program. Load a txt file. The text should appear.

Some changes that can be applied in the Properties window after choosing the textbox:
Scrollbars - adding a scrollbar if you have a lot of text loaded
CharacterCasing - turn all character into upper or lower case

In this application a person can start an "Openfiledialog" and then click cancel, the program will still continue with "a1 = File.OpenText... ". There won't be no text to open from a file. We have to limit the code to only do this part when someone actually chooses a file and clicks open.

The "OpenFileDialog1.ShowDialog()" should be changed to:
If OpenFileDialog1.ShowDialog() = DialogResult.OK Then

DialogResult.OK - function. You can write DialogResult. and then follow the menu list offered to notice all the other results. Examples: none, cancel, abort  etc.
If the person clicks Ok or "open" in this case - only then proceed with the rest of the code.

Final code:

  Imports System.IO

    Public Class Form1

        Private a1 As StreamReader

        Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

            If OpenFileDialog1.ShowDialog() = DialogResult.OK Then
                    a1 = File.OpenText(OpenFileDialog1.FileName)
                    TextBox1.Text = a1.ReadToEnd()
            End If
        End Sub

End Class

Start program. Open load screen. Choose cancel to see if the program will crash now. It shouldn't

We had to apply an if statement in the code. It has the conditions that must be satisfied in order to continue with the code after the Then expression.

When we use this application, we are able to choose all types of file into the loading screen and then click ok. So, you could load an ".avi" file into the loading screen or ".rar" file. How do you limit a person to stick to .txt files?

Go to the design page and then select the "OpenFileDialog1" element. Go to the properties window and find the "Filter" value. Add this there:
Text File(*.txt)|*.txt

"Text File(*txt)"  - this is just a name, you can change it as you like
"|" -> symbol for "and", press CTRL+ALT+W
*.txt - file extension that will be used (allowed) by the program

Start the program, click the button and go to the loading screen. Notice the file filter being present.
You can add more file types like this:
Text File(*.txt)|*.txt|Documents|*.doc|PDF Files|*.pdf
Or:
Text File(*.txt)|*.txt|All Files|*.*|

We can set the initial directory of our loading files.
Design tab -> select the "OpenFileDialog1" element -> Properties -> "InititialDirectory": write a file path