blockchains (e.g., those used by bitcoin or ethereum) enable two people or organizations to confidently and securely transfer value (e.g., money or a digital asset) electronically from one person or organization to another without an intermediary (e.g., a bank or PayPal).

a side note, technically, the blockchain solved the Byzantine Generals’ Problem, but since the question asked for problems it “generalizably” solves, this is very simple, non-technical answer.