about data feeds

First of all I would like to congratulate you for your site.
Second I would like to ask you where do you get the data about the positions of the planes(and if you can’t answer this question could you at least tell me if you have to pay to get your data?).
The reason for my question is that I wanted to code in my free time a program similar to flight explorer.

You should contact commercial services about this.

Thank you for the information.