I found this infographic from nextlingo on Pinterest. Ya and todavía can be very confusing. Ya can be used to say now, yet and already. Todavía can be used to say yet and still. As you can see, ya is used to indicate a change from the past to the present and todavía indicates continuity from the past to the present.
Here are a few more examples.
Ya viven en nuevo piso. (They’re living in a new apartment now.)
Ya ha olvidado lo que hiciste. (She has already forgotten what you did.)
¿Han llamado ya? (Have they called yet?)
No lo quiere todavía. (He doesn’t want it yet.)
Llevo trabajando todo el día y todavía no he terminado. (I’ve been working all afternoon and still have not finished.)
Ya and todavía have other meanings and uses, but this visual has helped me to begin to understand how to use these 2 adverbs. I hope it is helpful to you as well!