What does soldering flux paste do?

Could you elaborate on the purpose and functionality of soldering flux paste in a concise yet comprehensive manner? I'm curious to understand how it aids in the soldering process and what specific role it plays in ensuring a strong and reliable bond between metal components. Is it a necessity for all soldering applications, or is it specific to certain types of joints or materials? I'd appreciate a clear and concise explanation of its importance and how it contributes to the overall success of a soldering operation.