to summarize, I want to familiarize myself with the backend of apps but more specifically an app with these specifications: -The app opens up to a login/sign up page *the signup page has to store email, phone number, name, username, and a profile picture along with an accept services button. -it has to be able to take a purchase store a purchase history and then immediately put that purchase in a queue as well. Total users 30,000 concurrently active users 5,000 So that's a very quick summary. My specific questions are: what is CloudKit and how would it work with an app? Is there other services that I need? What's an SDK and does it helps storing user profiles? In general, what do I need on the back end to make this app work like servers, 3rd party services(prefer ably cheapest option? I'm totally new to all this backend stuff so I'd greatly appreciate an in depth answer or maybe a few sources linked!