There are a few different meanings for the term "just around the corner," and how it is used depends greatly on the context. One of the most common uses is to suggest that something is going to happen in a very short amount of time, usually something that people have been waiting for. Another common use is in reference to the distance from one place to another, suggesting that a location is close. It can be used in a literal way to give directions from one location to another when there is literally a bend in the road or a turn leading to the new location. A few common variations exist on this phrase including "just around the bend," which has basically the same meaning, and "round the bend," which references some level of insanity or eccentricity.
The literal meaning for this idiom is the one related to actual traveling or finding things, and the metaphor for the other meanings may come from the common human experience of going from one place to another. Often when traveling, it is possible to be very close to a destination without actually being able to see it. Someone might say, "Where is the store? I thought we were close," and the other person might reply, "Don’t worry, it’s 'just around the corner.'" In many cases, this might be said even if the store isn’t actually physically situated around a corner from the current location, and it may often be used simply to let another person know that the destination is very close, even though it may not be possible to see it yet.
In many cases, people use the term "just around the corner" in relation to time. This generally comes from the fact that time is often seen as a metaphorical journey with twists and turns just like a road, and the future is usually hard to predict, comparable in many ways to the experience of rounding a corner in a new location and seeing unexpected sights. If an event is just around the corner in the sense of time, it generally means that the wait won’t be long even though the event might not seem imminent. For example, a parent might say to his child, "I know it may seem like you’re gonna be a kid forever, but college is actually just around the corner." It can also be used in a more casual and less purposeful way to describe nearly any upcoming event in the near future.