What is the formula for match lookup?

Excuse me, could you possibly clarify what the formula for match lookup entails? I'm trying to grasp the concept, but I'm having a bit of difficulty understanding it. Perhaps you could break it down for me, step by step, so I can fully comprehend the mechanics behind it? I'm genuinely interested in learning more about this topic and how it can be applied in various scenarios. Thank you in advance for your time and patience.