Hello and welcome. Did you get it from an outfit like rv wholesalers or a dealership or what? Anywhere that sells them should have given you a pdi (pre-delivery inspection) that includes how to use it. That said I think it would behoove you to find d a local Thor dealership and pay them to do a walk thru with you. This way you can learn to use all of your systems and look for any issues to be repaired under warranty. Best of luck to you.
As Hoosierdaddy says the inverter is in the compartment on the drivers side. The control to turn it on should be above the control panel where you slide, light and level indicator is. I have a 2013 DT and my is there. Push the button to turn on.