If this is a message transfer, YMODEM SINGLE mode will be used,
 I will send the message in a single file called MSG.  I will collect
 the message first and will start sending as soon as I am ready.

 If this is a file(s) transfer, YMODEM BATCH mode will be used, meaning that
you do not have to tell your own system what the name(s) of the file(s) are.
I will start sending as soon as you let me know you are ready.
If you don't understand what you are doing, maybe you shouldn't do this.