Database is in another continent

multer to local server to cloudinary -- industry production grade settings used multer and cloudinary for file uploading will be using advanced mongodb aggregation pipelines

1. Deployment and ship to Prod
2. backend-frontend connection, CORS Error, proxies
3. HTTP
4. env variables, prettier setup
5. database connection in professional manner
6. setting up app.js for routing, setting up middlewares for urlencode, coookieparser, json, static files
7. mongoose models, pre hooks for "save"
8. Access Token, Refresh Tokens.
9. file uploads(multer and cloudinary) middleware
10. Auth middleware(JWT)
11. Controllers for user routesregister, login, updateprofile details, reset password, logout, get user profile,
12. MongoDB Aggregation Pipelines for watchhistory and list subscribers and subscribedTo. (JOIN operations basically)

For most of the database schemas, have clarity on Fundamentally, what are we supposed to do in a controller, What will user do when they arrive at the route, they take it(get) or give it(post), save(patch) and what is he requesting.

For line of code inside functions. question why it used the way it is. Better practices.