You press the " trigger" – the verb we would use is " pull" the trigger – in order to start the gun working.

您按下“扳机” ——我们将使用的动词是“拉动” 扳机——以启动枪支工作。

I tried to impress him and I backed off and I pulled out my teargas pen, and I pressed the trigger, and some ink trickled down my shirt.

我要给他点厉害看看，我后退一步，拔出我的催泪瓦斯笔，我按下机关，几滴墨水滴到了我的衬衫上。