There are a couple of tricks involved here. First is to avoid an error if the selection doesn't include any table elements. Second is to avoid having the end of cell marker as part of your string.
Code:
Sub Macro1()
Dim str As String, aCell As Cell
If Selection.Tables.Count > 0 Then
str = Selection.Cells(1).Range.Text
str = Left(str, Len(str) - 2)
End If
MsgBox "Text in first selected cell: " & str
End Sub