表达 “put pen to paper” 的意思是 “动笔，把讨论过或思考过的事情写下来”。

例句
I've been thinking about a great detective story for years, but I'm finally going to put pen to paper this weekend.
多年来我一直想写一个侦探故事，这周末我终于要动笔了。

The negotiations are over, and we now need to put pen to paper and make our deal official.
谈判已经结束了，我们现在需要付诸笔纸，正式签署协议。

I'll only put pen to paper and sign the contract when we've agreed my salary.
只有我们谈妥薪水后，我才会下笔签字。