Adverbs of time later is usually placed at the end or beginning of a sentence.
I will call you later.
Later, we went to the zoo.
It can also be placed after the main verb and usually has a function of comparative.
Our mail arrived later than usual.
YET is primarily used in negative and interrogative sentences. It is normally placed at the end of a sentence.
I haven’t had my breakfast yet.
Daren hasn’t gone to the dentist’s yet.
Have you finished your homework yet?
Have they decided about the wedding date yet?
YET can also be used in positive sentences to talk about a future possibility.
We might yet be able make a deal with them.
Things could yet improve in the company.
The adverb STILL is used to describe something that is happening continuously.
Tom is still thinking about moving to Corsica.
They are still not sure whether to continue with the project.
It can also be used with the modal verbs may, might, can, and could to describe something that was a possibility in the past, and which could possibly happen in the future.
We can still catch the 5.15 train.
I could still make it up to you.
FOR & SINCE
We use FOR & SINCE when we talk about how long something happens.
We use FOR with a time phrase that specifies a length of time.
I have been waiting for two hours.
Lorna has been studying English for five years.
We have lived here for 20 years.
We use SINCE with a specific point in time.
I haven’t eaten anything since 8 o’clock.
Bill has put on weight since he started working in that bakery.
They have been married since 2012.