Ideally you would install the IO adapter on the Unix box you intend writing to. The working/ completion directories are used for FilePoll operations - the file is picked up out of the directory you specify, moved to the working directory where it is actioned on, and dumped in the completion directory.
Take a look at the IO adapter user guide - it has fairly good explanations on how to use it - typically found in \doc\fileio, otherwise available from the bookshelf on this site.
You’d typically use a FilePoll operation to poll a directory for a file, and e.g. delimited input to action on the file. For writing the file, you’d use a FileWrite operation.
W
#webMethods#Adapters-and-E-Standards#Integration-Server-and-ESB