Kako si? means “How are you?”. The image is deliberately more elaborate than it needs to be: a generic party scene would later fit dozens of similar sentences, and the point is to be able to recall this one unambiguously.
You spot a winemaker among the vines in the distance, walk over and notice that he is drinking tea, eating at the same time, is rather heavy, and a radio is playing in the background. Those five details together stand for “How are you?”.
He tells you that he normally drinks cocoa, that it costs a fortune, and that he always pours it through a sieve. Cocoa, cost and sieve give you kako si. The cup in the image is unusually large – that is how you remember the stress falls on the first syllable.