@Musarrat Khan I would start at the bottom of the diagram and work your way up. Vnet -> VM -> App Gateway -> Traffic manager.
When deploying your VNETs, make sure they do not have an overlapping address range. Don't be afraid to try something and make mistakes, that is part of learning. Changing / re-deploying something is easy in the cloud.
If you need specific instructions, I would be happy to clarify any points or point you to documentation. I prefer Bing to Google when searching Azure documentation.