"just" has a few meanings. It can mean "only", or it can mean "very recently".
"We have just enough time to stop for pizza"= means you have only enough time to stop for pizza, but no extra time for anything else. Or "The pizza was just ok"= means it was not great pizza, it was edible but not especially good-tasting.
"I just came from the swimming pool"= means you were at the pool moments ago.
Or a third use, "Just do it!", means don't make any excuses, stop delaying, and simply do whatever it is that you are hesitating about.
In any case it denotes quickness, immediacy, or the bare minimum.