¿Cuál es la diferencia entre just y only ?Puedes dar oraciones como ejemplo.

"Just" has a unique sense: an adjective meaning morally or legally fair. "The ten year jail sentence was just".

"Only" has a unique sense: an adjective meaning singular. "He was the only man there".

In the sentence - "There was only two men there" only has a different meaning: "merely". Both words are also often used synonymously, with slightly different implications, for "merely". 

"He is only one man" or "He is just one man". They both mean the same thing - belittling the subject. Same with "Wait just a minute" or "Wait only a minute". They both belittle the minute as the smaller portion of an implied greater period. With the former "just" can be and should really be understood in its usual sense "exactly" - Using it as "merely" is an aberration of "just" that is widely accepted.

So "just" has a unique sense "exactly". "I got there just in time to see the whole wedding" means exactly on time. You cannot use "I got there only in time to see the whole wedding" because only means "a potion of". 

You would say "I got there only in time to see them kiss" and you could also say "I got there just in time to see them kiss". You would use the former to imply an unsatisfactory portion; the latter to imply you were happy with the best part. 

"There is only enough for two" or "there is just enough for two". In both senses there is an implied limitation but in the latter "just" means exactly, and "thankfully" is implied.