求指导!!!!!!!此程序是vb贪吃蛇上面的timer3代码是什么意思????

Private Sub Timer3_Timer()
p1 = p1 + 1
 p = p + 1
Dim i As Integer
 If p Mod 2 = 1 Then
  

For i = 0 To maxlong Step 1
 Shape1(i).Visible = False
Next i
Else


For i = 0 To maxlong Step 1
Shape1(i).Visible = True
Next i

End If
If p1 = 6 Then
Timer3.Enabled = False

'MsgBox "结束游戏!!"
End If
Screen.MousePointer = vbArrow
End Sub