Given circumstances are the conditions in which the scene happens: who the character is, what is happening, when and where it takes place, and why those facts matter.
Useful circumstances affect behaviour. Occupation may change what a character notices. Time period may change what can be said openly. Time of day may make a meeting unusual or dangerous. The immediate location controls privacy, distance, and intimacy. Pain, cold, exhaustion, or intoxication may create a physical obstacle.
You do not need to invent an answer for every possible question. Use this rule: if it is relevant to the story, it is relevant to you. For each fact, finish the sentence, “This matters because...” If the answer does not affect the objective, obstacle, relationship, risk, or action, put it aside until the scene gives you a reason to use it.