I work as a freelance developer.
I'd like found my own startup, but I don't know "anything" about economics and entrepreneurship.
Where can I learn basic economics as a developer to run my own company?
1. Learn to delegate. This is surprisingly hard at first, if you are used to do everything yourself.
2. Learn to motivate and inspire. You need to surround yourself with talented people who work toward common goal.
3. Learn to demand, when it's needed. People actually enjoy getting things done, but sometimes it requires that you push a bit.
4. Learn to make decisions quicker. Developers are analytical folk, so we usually err on the side of gathering too much information before making decisions. Sometimes it's more important to just make a decision with inadequate information and move forward.
1. Read. Books. I was the weird geek/programmer who always found business fascinating, so I've been collecting and reading books on business and marketing for years... going way back to before I launched Fogbeam Labs. A few titles you might want to consider, going from memory:
A. The Four Steps To The Epiphany - Steve Blank. This is about as close as you get to a "paint by the numbers" guide to launching a startup. Invaluable. I felt like Neo in the Matrix going "whoooah" after reading it.
B. The Startup Owner's Manual - Steve Blank and Bob Dorf. This is basically the 2nd edition of The Four Steps To The Epiphany but there is some difference in the content. I'd honestly recommend reading both, but if you're really more specifically focused on web startups / SaaS apps and the like, there is more for you in this book than TFSTTE.
C. The Art Of The Start - Guy Kawasaki. One of the "Bibles" of startup knowledge. I found this indispensable as well.
D. Running Lean - Ash Maurya.
E. The Lean Startup - Eric Ries
F. Forget me trying to compile this list from memory. Go to Quora and find the threads titled something like "What are good books for entrepreneurs to read". 
2. Mixergy.com - Read their freely available stuff, then join and read/watch/listen to the great content they make available.
3. The Stanford Entrepreneur's Corner - Lots of great videos and audio of presentations and what-not, on entrepreneurship. Freely available. http://ecorner.stanford.edu/
4. Take a few classes at your local community college if you have one. I went this route, and took Introduction to Business, Introduction to Business Law and Introduction to Marketing. Those three classes are a good foundation for some basic stuff you'll want to know. An accounting class might not hurt either. In the case of my local CC, these classes were all available as online courses, and were fairly inexpensive.
5. Your state government (I'm assuming you're in the US, if not, this might not apply) probably has something like an "entrepreneurship center" or something, that provides information on this topic, and holds seminars and helps out. Community Colleges also have similar resources. There are probably also non-profit advocacy and education groups dedicated to helping entrepreneurs. Here in NC we have things like:
Look for similar orgs in your area.
6. SCORE - a group made up of retired executives who provide free mentorship and advice to entrepreneurs. http://www.score.org
7. Steve Blank has a great blog with some great stuff. Here's an example of some good material from Mr. Blank. http://steveblank.com/category/lean-launchpad/
There are tons of resources to help you on this journey, and a lot of them are free. Dig in and take advantage. Obviously you found one great resource already, in HN, and there are a lot more out there.