Nevvur, don't you automatically know where the enemies are, except if they are actively hiding (which cost an action)?
Kinda. You'll find variation among DMs in how they adjudicate stealth. I think the part that confuses most new players (especially rogues) is the expectation they can hide, sneak up behind an opponent, and do a melee backstab. In 5e, everyone has 360 degree vision at all times, as far as the mechanics are concerned, making that impossible - unless the opponent is blind or something, but then you're already getting advantage, so being hidden en route to the attack provides no extra advantage, and then your location is revealed after the attack anyway.
At my table, if you were standing in a fog cloud and not doing anything, you're hidden (unseen and unheard, per the block I posted earlier), no stealth check necessary. Cast a spell with a verbal component? You're no longer hidden. Move a few spaces within the cloud on your next turn and quaff a healing potion? Hidden again. Holding a torch in the fog? I'll rule that enough light penetrates the mists to give enemies a good idea for your center of mass, so you're no longer hidden (though a clever player might create a light source in the fog away from himself so as to draw fire!). Shoot a bow or throw a dagger? Minimal sound there, and all it really does is suggest a line of travel along the arrow path. That doesn't strictly give away your position in my book, but it can certainly narrow down the guess work for an opponent who wants to fire into the fog from outside. Try the same thing with a firearm (if they existed in my setting) and your location is definitely revealed.
As Oofta said, the stealth rules are vague. Some DMs will try their damndest to squeeze some RAW out of it, but there are many, many strange scenarios the rules don't cover. I try to make the context of the encounter meaningful when adjudicating stealth, rather than rely on the rather skimpy RAW to resolve all situations.
My advice, save the fog cloud for out-of-combat scenarios and enemy spell casters.