Shoutbox

I'm very new to Visual Basic and I'm making a program that displays text after text in a label when you click a button...but the only code I know is how to make a text in a label change once...like this;

code:

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Private Sub Command1_Click()
Label1.Caption = "First Text"
End Sub

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Could someone tell me the code to make the text change once again when the button's pressed again...