How to find numbers from a string?

Assuming you mean you want the non-numbers stripped out, you should be able to use something like:

Function onlyDigits(s As String) As String
    ' Variables needed (remember to use "option explicit").   '
    Dim retval As String    ' This is the return string.      '
    Dim i As Integer        ' Counter for character position. '

    ' Initialise return string to empty                       '
    retval = ""

    ' For every character in input string, copy digits to     '
    '   return string.                                        '
    For i = 1 To Len(s)
        If Mid(s, i, 1) >= "0" And Mid(s, i, 1) <= "9" Then
            retval = retval + Mid(s, i, 1)
        End If
    Next

    ' Then return the return string.                          '
    onlyDigits = retval
End Function

Calling this with:

Dim myStr as String
myStr = onlyDigits ("3d1fgd4g1dg5d9gdg")
MsgBox (myStr)

will give you a dialog box containing:

314159

and those first two lines show how you can store it into an arbitrary string variable, to do with as you wish.

Regular expressions are built to parse. While the syntax can take a while to pick up on this approach is very efficient, and is very flexible for handling more complex string extractions/replacements

Sub Tester()
     MsgBox CleanString("3d1fgd4g1dg5d9gdg")
End Sub

Function CleanString(strIn As String) As String
    Dim objRegex
    Set objRegex = CreateObject("vbscript.regexp")
    With objRegex
     .Global = True
     .Pattern = "[^\d]+"
    CleanString = .Replace(strIn, vbNullString)
    End With
End Function