If your taxes are not being applied, then you need to check to make sure
your tax codes/tax groups are set up properly. It is possible that you have set
up your tax code so that only parts are being taxed, and labor is not – or vice
versa. Also you might have the incorrect tax code associated with the tax group
you are trying to assign. Another reason why your items may not show tax, is
that the tax checkbox on the work order’s general tab is still unchecked.

A schedule slot is a time slot for a work order.  You can have one or several slots of time for one work order.  A large job might take more than 1 day to complete and might require multiple techs to be scheduled.  You can create as many schedules slots as needed for a job/work order.   

Please click on this link.