tgt is just an alias for the table Sales data, you dont have to do it that way, just my habit.
N prefix makes the value that comes after it nvarchar. from MS
Prefix Unicode character string constants with the letter N. Without the N prefix, the string is converted to the default code page of the database. This default code page may not recognize certain characters.
lets say you want to do Dônà ètienne as the name, if your database does not have the proper code page, it might not update properly, you could get squares for those letters with diacritic.