a. Situations that continue to the present time. It is used in the past present or future. Still is placed in front of the main verb:
- It is still raining.
- I still live in London.
- They’ve been married for 30 years and are still in love.
- I still meet my friends from my schooldays now and then.
- Is your sister still at university?
- They are still living in the old farmhouse.
- We will still be at work when you arrive.
b. Action that is not expected because of something else
- He was sick but he still went to work.
- I studied a lot though I still didn’t pass the exam.
Still is placed after the verb to be and before an adjective:
- Her parents are still alive.
- We were unlucky with the weather in Greece but we were still happy with the holiday.
"Yet" is used in a negative sentence or in a question. "Yet" is placed at the end of a sentence or question.
To ask if something expected has happened.
- Have the test results arrived yet?
- I’m hungry. Is dinner already yet?
- Has she emailed you yet?
To say something expected hasn’t happened.
- I haven’t done my homework yet.
- It’s almost 11 o’clock and John hasn’t woken up yet.
- Kevin hasn’t registered for class yet.
- I haven’t finished my breakfast yet.
An action has happened sooner than expected.
- I have just finished lunch but I’m already hungry.
- I think Mary already knows about the surprise party.
- The plane had already landed when the pilot announced that there would be a delay in getting to the gate.
- There are already about ten people here
- We already knew that he was coming to visit.
- His family had already heard the news.
- Joe’s already here, so we can begin.
Already is placed after the verb to be and before the adjective like "still":
- Fifteen minutes after the play had started we were already bored.
- They knew that they were already late for the meeting.