Dreams are also different than visions, too. A person may call dreams "visions" ... but a dream can be nothing more than that... just a dream, even if Our Lord or Our Lady or some other holy person were in them. The bible itself tells us not to give credence to dreams. That's not to say it never happens. Obviously there have been rare exceptions when a person has received authentic messages in their sleep. But be they visions, dreams or anything else, only the Church is qualified to determine whether they're real (not just imagination, or simple dreams), and whether they're authentically something from heaven, or hell.
Among other things, though, you can sometimes tell if the "vision" or "message" has anything contrary to the faith, or does not sound like something Our Lord or Our Lady (or whoever) would really have said. Obviously, there are certain things or kinds of things that no one from heaven would ever say. Nor do visions typically puff up the visionary (Eg, telling them they're special or great or anything). And usually they sound a lot like the other known visions, with things like "pray for sinners" or some message that a certain devotion should be increased, or something like that. Generally speaking, persons from heaven don't just go around talking to people just to chat, to no purpose.
Ultimately, aside from the Church looking into them, it is hard to say, except that to some extent, by their fruits you will know them. Is the message contrary to the Faith or virtue or reason or anything we know as Catholics? Or does it puff up the person and make them brag and think they're special or "chosen"? Those are not marks of anything of heaven.
Lots of people claim visions or messages, but very often they're just victims of their own imagination, or some stronger delusion (like a mental illness), and that's all there is to it. Our Lord has already made it pretty clear what we have to do to save our souls. He has also asked (through Mary) that Russia be consecrated, which the world has not heeded. Finally, Mary has made known far and wide that all of us are to pray the rosary, and especially pray and make sacrifices for the conversion of sinners and for the poor souls. Since we know all of that already, what need would heaven have of having someone coming constantly to talk to someone?
I think if it were important, it wouldn't have taken someone from heaven anything like "someone's whole life" to tell them what needs to be said, or to encourage them to get on with whatever the purpose of the vision was (encouraging people to pray, to do some devotion, whatever). Certainly, I can't recall any saint's life, where they had visions "just because", that were to no real purpose. Persons from heaven don't typically come just to hear themselves talk.
The person in question really needs to consult a Catholic priest, not to just spout "information" from visions that COULD, for all they know, be from hell rather than heaven. By "not bothering with formalities" (talking to a priest, getting them approved, etc.), what they are doing by sharing the information of those "visions" is dangerous and irresponsible at best, since it COULD be the devil. And if they are Catholic, and don't want to suffer through being doubted by the Church, well... from what I know everyone whose visions WERE authentic did usually suffer that way, and in other ways, besides, but it was nevertheless necessary, for the good of the faithful, to know for sure where the visions in question came from, even if the visionary had much to suffer in trying to prove them.