Tasks are alot simplier then jobs. For example a job might be that a client has called up with a faulty sink (if you were a plumber), so the job needs to be scheduled, someone needs to go and fix the sink, and at the end an invoice needs to be raised.
A task for example, could be you are low on stock and need to remind yourself to order more parts, or if you have sent out a quote to a client, a task could be to ring the client in two weeks and see if they are still interested.