HTTP1 is simple and easy. With enough care you can open a TCP connection and hand-write an HTTP request to a server and get a response. Good fun. HTTP2 is more complex. Multiple bidirectional requests can be multiplexed over a single connection. You might use it with something like GRPC, or to get web pages to load faster. HTTP3 is wild stuff. Implemented over UDP instead of TCP. You can open a connection, open streams on that connection, send data with different types of ordering and deliver...
