I read that they have some uses within online encryption, but to be honest I never really thought about why we learned them in school until this morning.
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most common actual use case is credit card security/ bank account security.
The reason being, that you can multiply prime numbers really fast (like any other numbers multiplied are fast on calculators/computors) generating a security number (easily spoken).
However, if you have only that security number, but want to know out of which numbers it has been muliplied, computers need a lot of time, since divisions are more complex.
So it is easy if you know what the base (prime-)numbers are, but very hard if you want to find them. That makes them perfect for security.
And if you take large prime numbers or more of them that can be enough to increase the calculation time it takes a computer to crack it into years.
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