Can you tell me simple circuit so I will try to convert circuit into double sided PCB
What exactly is your problem?
- how to use pcb layout software?
- how to make a double sided pcb?
There is no special or explicitly simple circuit for either single sided or double sided pcb layout. You can make a double sided layout from almost any design (provided it is not too complex for 2 layers which means it requires more than 2 layer - that is of no concern here).
You could start with a single resistor connected to two terminals, one connection using the top layer, the other connection using the bottom layer. This I would consider a most simple "design" although it is rather meaningless. A circuit that is also rather simple but at least creates a little effect is an astable multivibrator,
e.g. this one (used to be kind of a "hello world" project for aspiring electronics hobbyists). You have crossing connections here which can easily be made using two sides of a pcb (although it wouldn't be strictly required here, but you're looking for an exercise).