I've been programming for years, and I've also done a few professional programming projects. I recently had a friend ask about creating an e-commerce site, but I had to turn her down because I had never worked on a web application that can bill. I also might need to write a subscription-based web service in the future. My question is, how do I even get started with billing? I've never found a guide about this, and I barely know how bank accounts work since I don't manage my own one (I have an excuse for this since I'm only 16).
I don't know if the answer is language dependent, but if it is the languages I'm interested in are Python, C/C++, and Java.
There are lots of ways to go about setting up e-commerce sites;
If you don't have any experience whatsoever, and don't want to get into anything "complicated", i would suggest going with a customizable web "storefront" hosted by someone else, pre-integrated with credit card processing, etc. There are tons of options for these online. Just search google for "web storefront". Yahoo! even has such a service:
http://smallbusiness.yahoo.com/ecommerce/sellonline.php
Going beyond that, It's pretty easy to integrate with someone like PayPal. They have all sorts of options from the most basic (use a link to send someone to their site with query string parameters to let paypal know what the user wanted to buy):
https://cms.paypal.com/us/cgi-bin/?&cmd=_render-content&content_ID=developer/home
Beyond that level, you will need to signup for a merchant account, or other similar sort of service, like the one offered by authorize.net (who I like):
There are components you can buy for most major web development platforms like .NET, JSP, etc. Perfect example is dotnetcart. These components provide out-of-the-box, easy-to-setup integrations with major CC processing companies, as well as out-of-the-box shopping cart implementations:
Finally, most merchant services / payment gateways provide web services for direct integration.
PS.) Never ever ever store CC numbers ; )