You can't just send data "to the net". You send data to some application running on a server.The app can be a PHP script, or a REST API, or something else. But, you have to know which server, and which application, you want to send the data to (and what format the app expects the data in).
I suggest that, as a start, you forget about the Arduino. Figure out the server and application and data format issues, and how to send data to the server using your PC. When you understand the whole process, making the Arduino, wearing an ethernet shield, do the same thing would be the next step. Next up, in terms of complexity, is doing the same with a WiFi shield. Top of the head, in terms of complexity, is doing it with a GSM shield.
Given your apparent level of understanding, I'd say that trying to learn everything using the Arduino with GSM shield is going to be next to impossible.