Tasks can have one or more of the following elements:
source host
Files are retrieved from all sources before any files are processed or sent to their final destinations
process
The process is run against all files that have been retrieved
destination host
All files that have been retrieved are sent to all hosts
schedule
The task runs at all of the times specified by all of the schedules

If a task has more than one...

What happens when the task runs:

source host

Files are retrieved from all sources before any files are processed or sent to their final destinations.

process

The process is run against all files that have been retrieved

destination host

All files that have been retrieved are sent to all hosts

schedule

The task runs at all of the times specified by all of the schedules