to explain something in a very clear way with details解释清楚;详细地说明
The government has so far refused to spell out its plans/policies.政府至今拒绝透露详细的计划/政策。
informal What do you mean you don't understand - do I have to spell it out for you?你说你不明白是什么意思——需要我详细地向你解释一下吗?