write it down：把它写下来
down：（写）下,（记）下
例句：
Anytime you write something down, it makes it a more permanent goal.
任何时候只要你写下想的事情,它就能变成长期目标.
When he took out a piece of paper to write something down, the paper was wet and then he knew that it was raining.
当他拿出一张纸来记下什么的时候,纸都是湿的,他这才意识到天下雨了.
Need to write down something but have no paper?
需要的东西写下来,却没有文件?
I want to write down something happened recently.
心血来潮想在这上面写点最近发生的事情.
Here is VIP space for you. Write down something please.
这里是为阁下特别预留的贵宾位置,恭请阁下留下墨宝.
希望能帮到你