Can anyone explain for me this code i can`t understand it ....

Code:
  Sub dimSquare()
        If xUp < 0 Then xUp = 0
        If xUp > 600 Then xUp = 600
        If yUp < 0 Then yUp = 0
        If yUp > 480 Then yUp = 480
        intW = Math.Abs(xUp - xDown)
        intH = Math.Abs(yUp - yDown)
        If intW > intH Then intW = intH
        If xUp < xDown Then intL = xDown - intW Else intL = xDown
        If yUp < yDown Then intT = yDown - intW Else intT = yDown
    End Sub
    Sub dimRectangle()
        If xUp < 0 Then xUp = 0
        If xUp > 1000 Then xUp = 1000
        If yUp < 0 Then yUp = 0
        If yUp > 480 Then yUp = 480
        intW = Math.Abs(xUp - xDown)
        intH = Math.Abs(yUp - yDown)
        If xUp < xDown Then intL = xDown - intW Else intL = xDown
        If yUp < yDown Then intT = yDown - intH Else intT = yDown
    End Sub
    Sub dimCircle()
        If xUp < 0 Then xUp = 0
        If xUp > 600 Then xUp = 600
        If yUp < 0 Then yUp = 0
        If yUp > 480 Then yUp = 480
        intW = Math.Abs(xUp - xDown)
        intH = Math.Abs(yUp - yDown)
        If intW < intH Then intW = intH
        intL = xDown - intW
        intT = yDown - intW
        intW *= 2
    End Sub
    Sub dimEllipse()
        If xUp < 0 Then xUp = 0
        If xUp > 600 Then xUp = 600
        If yUp < 0 Then yUp = 0
        If yUp > 480 Then yUp = 480
        intW = Math.Abs(xUp - xDown)
        intH = Math.Abs(yUp - yDown)
        intL = xDown - intW
        intT = yDown - intH
        intW *= 2
        intH *= 2
    End Sub