Vehicle Maintenance allows you to see what vehicles you have available for you jobs by removing the ones out for maintenance out of the booking board for that day.
Go into the Vehicle are on the side tool bar
On the top tool bar you'll find Vehicle Maintenance
Create new and select the Vehicles Registration. Select the dates that the vehicle will be out, this will remove it from the bookings board on those dates.
By clicking into a vehicles overview you can review if they have maintenance scheduled or when they were out for maintenance in the past.