I want to know how login works on web page in details.

Questions:

1. What happens when we use POST method. Is all the data encrypted before sending over internet. Can someone extract the information before it goes to web server. How POST is implemented?
2. How a password field work on a form, especially on login page? Is all the character entered in password field encrypted before sending to the server.
3. As a developer can I read password field using ASP or CGI.
4. How do I trust that e.g. a banking site developer or implementer cannot read my password using any code?