Principles

The main thing you need to know about internet is that despite you might be in your /home, in your office ..., the site you are naviguating on are located worldwide. That means that each manipulation you make on Internet is made outside your computer and that it could potentially be recorded.

When your browse a web site the process is the following:

The second thing you need to know is how a web page is generated. A web page could be static like a book but most of the case this is a dynamic web page. A dynamic web page means that the page is generated specifically for YOU. It works the following way:

You contact a front end server which contact a backend server which stores all the data in a database. The front end server then generates the pages with the data you feed in and the data stored in the database. The data you feed in like your credentials, your photos, your emails, are then stored in the server database located outside your house, and maybe outside your country.

Documentation

Internet Protocol, Wikipedia EN: http://en.wikipedia.org/wiki/TCP/IP

Internet Protocol, Wikipedia FR: http://fr.wikipedia.org/wiki/Suite_des_protocoles_Internet