Hi Eddy
That's a very simple command button click event

Private Sub btnOpenFolder_Click()
  Shell "EXPLORER.EXE C:\Users\USERNAME\Documents\", vbNormalFocus
End Sub

Replace folder name where necessary and there are different types of focus for the window to open in.
There is an article in the VBA help section if you want a further read.

Open Word:-

Private Sub btnOpenWord_Click()
    Shell "WINWORD.EXE"
End Sub

Open Word File:-

Private Sub btnOpenWordDoc_Click()
    Shell "WINWORD.EXE C:\Users\...\FILENAME.docx", vbNormalFocus
End Sub

Richard shows us the Shell command in VB201

Other Mentions
A useful one from Alan

Just search for shell in the header and there a few mentions throughout the forums.

Al