Maybe seeing their references may help you: JUST - only, simply "It was just a joke." "She lives just down the road (= very near)." "His daughter's just a baby/just a few weeks old." JUST - used to make a statement or order stronger "It's just too expensive." "He just won't do as he's told." JUST - used to reduce the force of a statement and to suggest that it is not very important "Can I just borrow the scissors for a second?" "I just wanted to ask you if you're free this afternoon." ONLY - used to show that there is a single one or very few of something, or that there are no others "I was the only person on the train." "Is this really the only way to do it?" "The only thing that matters is that the baby is healthy." "It was the only thing I could do under the circumstances." You see, 'just' you can use for different contexts, whereas 'only' is more specific. However, in some cases, as @dancingbear wrote, they are perfectly the same.

Sometimes it's the same. But sometimes just can also mean "simply" or something similar. It's a little bit like you want to end the conversation about the topic and move on. Just do it. I don't want to talk, just go away. I'm tired, just make me some dinner. Just shut up. I'll just sit here and think for a while. I don't want to go out, can't we just stay home tonight? Just can also be used for something that happened a while ago. "I just did that" "I just finished my homework"

Just and Only are two words in English that have to be used carefully so that their meanings are distinguished well indeed. The word ‘just’ means ‘a moment ago’ as in the sentence ‘Albert just left his home’. It only means that Albert left his home a moment ago. On the other hand the word ‘only’ indicates the lone object, thing or person left out as in the sentence ‘Johnson is the only boy in the class who secured distinction in the exams’. Here you would understand that Johnson is the lone boy in the class to have secured distinction in the exams. It is interesting to note that in American English the past tense is meant by the usage of just as in the sentence ‘He just went out’. Observe the sentence ‘Florence just had a conference talk with her colleagues’. In this sentence you can see that the word ‘just’ is used to indicate past tense. The word ‘only’ is used on the other hand to lay emphasis on a person or a thing as in sentences 1. Only Francis in the group knows the truth. 2. Winston is the only boy in the class who is taller than Francis. In the two sentences you can see that the word ‘only’ is used to lay emphasis on two persons, namely, Francis and Winston respectively. If the word ‘only’ is used in the end of a sentence, it gives an extra meaning altogether as in the sentence ‘Out of all the questions he answered a few only’. In this sentence the word ‘only’ gives the extra meaning that he did not know the answers for the other questions or found the time to answer them. Sometimes the sentence can be rewritten as ‘Out of all the questions he answered just a few only.’ lol.. http://www.differencebetween.com/

The words "just"and "only" sometimes carry the same meaning...not always. I have just three dollars. I have only three dollars. Same, same.