Firebase firestore functions

I am developing a web app using firebase and I use cloud firestore for it.I have a specific feature to be built that requires firestore functions. I need someone to help me with writing the few lines I am developing a web app using firebase and I use cloud firestore for it.I have a specific feature to be built that requires firestore functions. I need someone to help me with writing the few lines of code for this feature and also teach me about the same.The webapp already has a few features.For someone who knows firestore fu...