To schedule a job simply select it in the job list and then double click on the vehicle/driver in the list part of the schedule you wish to assign it to. As long as there are no jobs already scheduled with which this new one will conflict a new coloured bar will be drawn.
If you have chosen not to display scheduled jobs in the job list the entry that you have just scheduled will be removed from the list. If you have chosen to display scheduled jobs as well then the icon for the job list entry will change from a cross to a coach.
If you are trying to schedule a job to a vehicle or driver which is already assigned to another job then a conflict will occur. ph28 allows the user to decide, via the Conflicts tab in the Schedule Properties page, a conflict is to be prevented altogether or if the user can make a decision to allow the conflict to stand.