How to use openssl for encryption?
Put simply: Don't.
Use HTTPS instead of relying on application layer cryptography for this specific use-case.
Unless you are a professional cryptographer with a specific use case for why you wish to avoid TLS (with public key pinning) and have a plan in place to manage encryption keys, you probably shouldn't write your own cryptography. Or if you do, don't deploy/publish it.
And if you do find yourself needing to encrypt information at the application layer (there are many valid use cases for encryption here), learn all the pitfalls that you will encounter and maybe consider using libsodium instead.