log service task is used in same way as any other task. The only thing required for it is to define data input for it that you want to trace (log). Please remember that you need to define work item handler for Log service task - usually it is SystemOutWorkItemHandler class but you can provide your own that will use some logging framework instead os sysout e.g. log4j
I have defined the work item handler,but I don't know how to use this service in detailes.and I also want to know where to find the log.