Do loops are used to repeat some event until some action happens which is going to stop the loop.This loop will loop until or while that action has happened.It is mosy often used when we don't know how many times we want something to happen but it depends of the user or smth. else.
Code:
Do While Form1.Top < 5000
Form1.Top = Form1.Top + 20
Loop
This will move the form down while its top position is smaller than 5000.
Code:
Do Until Form1.Top > 5000
Form1.Top = Form1.Top + 20
Loop
This does the same thing just instead of while we use until.