A route consists of one or more turnouts or sensors that you would like to control. Before creating a route, you should first add some turnouts or sensors by using either the turnout table or sensor table. These tables can be found under the main menu "Tools -> Tables".
Once you have some turnouts or sensors to manage use the "Add" button in the lower left hand corner of the route table to create a new route.
Note that this doesn't remove the route from any files you've saved that contain it. If you load one of those files, perhaps when you restart the program, the route will reappear. You should use one of the "Store to file" options in the "File" menu to save new versions of any files that contain this route.
The turnout lock feature allows you to selectively disable accessory (turnouts) commands from cabs and/or locally-wired pushbuttons. JMRI disables pushbuttons by sending pushbutton disable commands to the turnout decoders when the route is locked, and enables the pushbuttons when the route is unlocked. When locking a turnout from cab commands, the JMRI program will monitor the turnout's accessory address and if it detects a change command from a cab, will cancel the command immediately by sending out the opposite command to the turnout. All turnouts that are being monitored by the JMRI program and are included in the route will be locked.
To help you select a set of turnouts to lock or unlock, a route can be locked or unlocked. In the route edit window, an optional lock control turnout is available. You can use the lock control turnout to enable or disable the route lock function from a panel turnout icon, a layout turnout or a phantom turnout. A phantom turnout is a turnout that can be accessed by your cab but doesn't actually exist on your layout.
For more information on how to set turnouts to be lockable, please see the Turnout Table page.