I have a very strange exercise from school and I can't figure it out. I am supposed to change this class diagram (shown on picture) to sequence diagram. But it just doesn't make sense for me as long as it seems that this picture describes just one class.
As commented you can not really convert it, just invent an example. Since it looks like this is a Facade implementation, a good guess would be the following:
You can see that calls to the Facade
are forwarded to the subsystems.