"Here is the situation." "Let me tell you about the circumstances."

Colloquially it's used as a contraction, "Here's the deal". It can be used when you want to tell a certain thing that either the person may not want to hear, or you can talk about an actual 'deal'. It's kind of like "Here's the thing...." EXAMPLE: Friend 1: Hey, can you give me a ride to my uncle's house" Friend 2: So here's the deal, my car is still in the shop for the next 2 hours; if you want to wait with me, I can drive you. It's only really used in conversation or very informal writing, like texting.