get something straight 把事情说清楚；弄清楚；搞懂

【例句】
Let's get something straight: I give the orders around here.
让我们弄清楚，是我在这儿指挥！

First of all, let me get something straight: This is a Journal, not a diary.
首先，让我把话说明白：这是一本日志，不是日记。