How to Write a Crowd Function in Firebase?

The first course on how to build a commerce application is now out. The second one takes that as a starting point and it goes into, how do you integrate this with fire base? And i mean, the basics will always be, how youat lockingand and ta. But that's the easy stuff. Then you get into some cod maybe shou run on te client. Some cose you run on the server. So in which case should you write crowd functions? What is their purpose? What should they do? A techniques for deciding, for example. It is quite uninteresting part that i will call in detail, an obvouy clod function survey.