Next.js is one of the most confusing technologies for me, i can't understand how it works on the server, how a server knows we need to achieve server side rendering with files created by Next.js in the build time?
I understand the client part, but how a server know that we need to achieve server side rendering after deploying the website files created by Next.
What is the difference between a React project created without Next.js in which the server send an empty HTML document in response to a client request, and a React project created with Next.js in which a server will send a full document to the client??
how a server knows we need to achieve server side rendering with files created by Next.js in the build time?
Have you taken a look at the Next.js server-side rendering documentation here?. There is more about static generation here.
Also for more on server-side rendering, check out this site
What is the difference between a React project created without Next.js in which the server send an empty HTML document in response to a client request, and a React project created with Next.js in which a server will send a full document to the client??
Not entirely sure with the wording here, but if you are asking what Next provides, it is a framework that will give you everything listed on their landing page that you would have to code up or figure out otherwise. They provide a quick way to wrap up and generate production-ready files to deploy.