I haven’t finished eating yet.

It cannot be used for the future, and it is usually placed at the end of a sentence.
• Agnes can’t go home, she hasn’t finished her work yet.
• They haven’t paid me yet.
• John will be here yet.
(Cannot be used for the future)
• It’s nearly 8 o’clock – John will be here soon.
(Means the plan was for John to arrive at 8pm so he is not late)
• It’s 8.10 and John isn’t here yet.
(Means the plan was for John to arrive at 8pm so he is late)