How do HTTP sessions work?

An HTTP “session” is a technique for preserving data between HTTP requests from the same user. Since HTTP is a stateless protocol, there is no protocol-specific way for a server to know if two incoming requests are from the same user.

Developers use the technique of “sessions” to save data that should be preserved between multiple requests from the same user such as their name or their setting preferences (e.g., dark vs light mode).

See this link for a visual illustration.