You need to create the folder in the examples folder in the inet framework (i do not know if it is the good framework for ring, bus, .. you have to research on the net if this framework allows to do these topologies) !!
You create the ned file and the omnet.ini (for that file->new-> file ini or file ned)
In your ned file, it depends on what you want to do !!
I suggest you to see in examples folder and take inspiration from it. And the omnet.ini you only put the values of parameters defined in the ned file in order to create your scenario.