Hey David! I shall provide you with an explanation about the difference in usage between ''yet'' and ''already'' in sentences, as follows;
--> You use 'yet' in negative sentences to say that something has not happened up to the present time, although it probably will happen. In conversation and in less formal writing, you usually put 'yet' at the end of a clause.
E.g.: ''It isn't dark yet''.
E.g.: ''I haven't decided yet''.
--> In formal writing, you can put 'yet' immediately after 'not'.
E.g.: ''Computer technology has not yet reached its peak''.
E.g.: ''They have not yet set a date for the election''.
* ''HAVE YET TO...'': Instead of saying that something 'has not yet happened', you can say that it 'has yet to happen'. People often use this structure to show that they do not expect something to happen.
E.g.: ''I have yet to meet a man I can trust''.
E.g.: ''Whether it will be a success has yet to be seen''.
** ''JUST YET'': If you don't intend to do something 'just yet', you don't intend to do it immediately.
E.g.: ''It is too risky to announce an increase in our charges just yet''.
E.g.: ''I'm not ready to retire just yet''.
--> You use 'already' to say that a situation exists at an earlier time than expected or that something has happened before now.
E.g.: ''She already knows the answer''.
E.g.: ''He had already left when I arrived''.
*** NOTICE (USAGE IN QUESTIONS):
--> You often use 'yet' in questions when you are asking if something has happened. You put 'yet' at the end of the clause.
E.g.: ''Have you had your lunch yet?'
E.g.: ''Have you done your homework yet?''
--> Do not confuse 'yet' with 'already'. You use 'already' at the end of a question to express surprise that something has happened sooner than expected.
E.g.: ''Is he there already?''
E.g.: ''You mean you've been there already?''
Hope that helps! :)