关于VB的问新手题

想请问一下为什么有的VB程序里会加这么一段，，这是什么意思？？他又有什么作用？？求解，谢谢了
Public Const WH_KEYBOARD_LL = 13
Public Const WH_MOUSE_LL = 14

Public Const VK_LWIN = &H5B
Public Const VK_RWIN = &H5C

Public Const HC_ACTION = 0
Public Const HC_SYSMODALOFF = 5
Public Const HC_SYSMODALON = 4
Public Const WM_KEYDOWN = &H100
Public Const WM_KEYUP = &H101
Public Const WM_SYSKEYDOWN = &H104
Public Const WM_SYSKEYUP = &H105

Public Const WM_LBUTTONDOWN = &H201
Public Const WM_LBUTTONUP = &H202
Public Const WM_RBUTTONDOWN = &H204
Public Const WM_RBUTTONUP = &H205

Public Const WM_MOUSEMOVE = &H200