请问该语句是什么意思？？？

Public Declare Function MessageBox Lib "user32" Alias "MessageBoxA" (ByVal hwnd As Long, ByVal lpText As String, ByVal lpCaption As String, ByVal wType As Long) As Long


百度了也没有搞明白，望赐教啊，谢谢啦！！！

api

Public Declare Function MessageBox Lib "user32" Alias "MessageBoxA" (ByVal hwnd As Long, ByVal lpText As String, ByVal lpCaption As String, ByVal wType As Long) As Long


user32 DLL里有函数MessageBoxA ,重新定义为MessageBox 
括号里是参数
hwnd 句柄
lpText 内容
lpCaption 消息框标题
wType 消息框类型

返回 Long


MessageBox Me.hwnd, "aaaaaaaaaaaa", "提示", 0