It has to do with expectations. If you're dealing with an expected outcome, use yet. If you're dealing with an unexpected outcome (or describing a continuous action), use still. "I thought the mailman would be late due to the snow, but my package still arrived on time!" "Though the expected arrival was today at 4:00, my package still hasn't arrived yet!" You see can that in the first sentence, still is used because the package arriving on time was unexpected due to the snow. However in the second sentence, it was expected that the package would arrive on time, as there was no reason it shouldn't have, so yet was used.

Still is commonly used when refering to something that is still in "action". "The computer is still working." "It is still raining." Yet is used for something that hasn't happened. "The computer has yet to work. "It is not raining yet. haha even to a native english speaking its a little tricky but i hope that helps.