To see your work orders, navigate to Unit Details > Maintenance in the menu.
This will bring up the Maintenance page where you can select a unit and view all the work orders for it. You can change the date range to see past or future work orders.
To add a new work order, click on the blue "Add Work Order" button on this page. From here, fill in all the info in the popup menu that comes up:
Select the unit, select the correct date range for this work order to take place in, the subject of the work order, and any comments that are relevant. Then click the blue "Add" button.
In the maintenance menu, active work orders will show as green, and past work orders will show as red.