On Error Resume Next causes execution to continue with the statement immediately following the statement that caused the runtime error, or with the statement immediately following the most recent call out of the procedure containing the On Error Resume Next statement. This allows execution to continue despite a runtime error. You can then build the error-handling routine inline within the procedure. An On Error Resume Next statement becomes inactive if another procedure is called, so you should execute an On Error Resume Next statement in each called routine if you want inline error handling within that routine.
The VBScript object Err can be used for detecting the error and its description. The usage is demonstrated in an example.
On Error Resume Next
Dim a, b
a = 0
b = 1/a 'Division by zero !!
If Err.Number <> 0 Then
MsgBox("Error=" & Err.Number & " Description=" & Err.Description)