Natural stones protect on the balcony

Hi everyone,
we have bought a new apartment.
There are natural stones on the balcony (in my opinion) and you can see every stain that is difficult to remove.
How can I protect them and apply some kind of protective film so that they can be cleaned easily?

What do you mean by natural stone, those are concrete slabs. Normally, they should have a certain impregnation from the factory. But it can also be applied afterwards, of course it's questionable how good that will be. Go to the hardware store you trust.