Not as simple as it may sound. First of all, you probably have the same brown common snail that I've got - a quick search gives
this
They aren't, as such, bad for the fish. However, they eat plants (and that's how I got them, eggs on a plant at some point), and they poo/pee in the water (just like fish), so they add to the "bioload" and adds to the nitrate levels in the tank.
If you have cory's (or other fish) spawning in the tank, the snails may also eat the eggs...
If you have a relatively constant population, it's not a big problem - but if there's nothing in the tank that eat young snails or the eggs, then you'll have an ever increasing population... Which is not a great thing...
So whilst the snails individually aren't a bad thing for the fish, the huge number you'll get after a while will possibly cause a problem.
There's a few things you can do:
1. Ignore it - it won't go away, but if you're OK with keeping a bunch of snails as well as fish, it's not a big deal.
2. Get some snail-eating fish - there's been several discussions on this matter in the forum, so a Forum Search on "snails" would probably yield some useful tips.
3. Chemical warfare - there are chemicals that will kill snails - typically those containg copper in some form. However, you should be prepared to repeat the process several times, because very often, the eggs will not be affected, but only the "born" snails.
4. Pick the snails out by hand - trapping them using a piece of vegetable or such works quite well and helps getting lots of them at once rather than hunting around every corner of the tank.
I personally don't like #3, and I see that as a last resort.
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Mats