A smartlist is a saved search. Whether or not a file appears in a smartlist, depends upon whether or not its tags satisfy the search criteria.
If you want all files within a particular folder to be included in a smartlist, then you would set the rule for that smartlist to match on the library field [Filename (Path)]. Then as files are added to that folder, and subsequently imported, the filename path matches the rule and the new files appear in the list.
The critical thing here is that in order for most smartlists to function as you would expect them, the library tagging has to be correct.
Perhaps if you let us know exactly what you're trying to achieve, we can help you reach your goal, and at the same time, help you arrive at some understanding of how you got there, which would get you a kick-start up the learning curve.
-marko