Gennaro is on the right track, but both can be used in the negative. YET is usually used for something you're waiting for or expecting, but that hasn't happened so far. (The parcel hasn't arrived yet.)....I am waiting for the parcel to arrive. (I haven't had time to sit down yet today.)....I expect to be able to sit down today, but it hasn't happened so far. (Have you finished it yet?)....I expect you to finish it soon, but am unsure whether you have done. STILL Is usually used for things that started in the past and are continuing in the present. (I had lunch, but I'm still hungry).....I've eaten, but the hunger continues. (Do you still want to play tennis on Saturday?).....You said you did yesterday. Does that continue to be true? STILL AND YET Still CAN be used in a negative statement, meaning that the action that didn't happen in the past is continuing not to happen in the present. I haven't had dinner yet. I still haven't had dinner. My mother hasn't called yet. My mother still hasn't called. They are really useful words, Jorge. I hope you enjoy using them!

Very quick ... use still for positive sentences I still learning English ... Yet for negative sentences I didn't get my gift yet