Newbie here, so forgive me if this is a stupid question. In math class we learned about RSA encryption (as a practical application of what we learned about the Euler phi function and Fermats little theorem), and I wondered that since the same input always yields the same output, if eve had a couple of guesses for what the message is (for instance a yes or a no), she could try encoding them herself and compare that to the ciphertext. I googled how to get around this, and I gathered that a process can be non-deterministic, meaning it yields different results if done repeatedly. However, when I looked into how this was possible, I never really understood the explanations, they got really complicated really fast.
So what I'm asking is, can anyone explain fairly simply (high-school level math) how a ciphertext can be generated with an element of randomness, but still be decipherable. Surely the receiver can't easily undo those random changes, if the same message could come in in many different forms?