You can set the help context ID for a command button and then when a user presses the question mark on the user form then the command button they would get the help text.
If you want to just open the entire help file from a button try this:
Option Explicit
Declare Function ShellExecute Lib "shell32.dll" Alias "ShellExecuteA" ( _
ByVal hWnd As Long, _
ByVal lpOperation As String, _
ByVal lpFile As String, _
ByVal lpParameters As String, _
ByVal lpDirectory As String, _
ByVal nShowCmd As Long) As Long
Sub OpenAnyFile()
Dim FilePath As String
Dim FileName As String
Dim FileToOpen As String
FilePath = ThisWorkbook.Path
FileName = "FileName.hlp"
FileToOpen = FilePath & "\" & FileName
Call ShellExecute(0, "Open", FileToOpen & vbNullString, vbNullString, vbNullString, 1)
End Sub