Let me introduce you to one of my pets, a guinea pig called Beba. If it is a boy or a girl, you'll find out in our future lessons with it :)
The idea is for you to practice this short dialogue asking each other what you are having for breakfast:
a: Šta radiš = What are you doing?
b: Doručkujem = I'm having breakfast.
a: Šta doručkuješ? = What are you having for breakfast?
b: Doručkujem (travu) = I'm having grass for breakfast. (trava = grass)
For this, you'll need some knowledge about food & the accusative case. I'm sure this video will help: