How do I get value of a multi-selection form listbox?

I've never used the form listbox before. I've always used data validation list.

How do I get the selections into my macro? I have my macro putting the listbox into an object, but I can't find a value.

Sub ListBox_Selection()
    Dim s As String
    Dim sh As Worksheet
    Dim o As Object
    
    On Error Resume Next
    s = Application.Caller
    On Error GoTo HE
    
    If s <> "" Then
        Set sh = ActiveSheet
        Set o = sh.ListBoxes(s)
        'how do I get the selections?
    End If
HE:
End Sub