ActionScript 3.0 :: Using Classes To Add Code Instead Of Adding It Directly In FLA File

for first time decided to start using Classes to add my code instead of adding it directly in Flash and I really thought I knew how to handle this since I have created some re-usable classes before where you target an object by passing parameter etc,I thought that if I had one function (method) in my class and I wanted to call it from my .fla file all I needed to do was to create an instance of the class and then call my method.[code]But this doesn't work I get a message that says that it is missing arguments.how to use my code directly on a class and what are the differences of doing this versus putting the code directly on my .fla file and if it's even a good practice to do this?