Inside the GPL: Tip Sheet
The GPL doesn't contain restrictions on how software is to be usedjust how it can be distributed, copied, or modified. Specifically, the GPL requires the following:
Any software distributed under the GPL has to be accompanied by the text of the GPL, unmodified in any way.
Software distributed under the GPL can and should contain copyright notices of the original author.
If you distribute software under the GPL, you have to provide a way (electronically and mail order) for people to obtain the source code.
If you modify a program covered by the GPL, you have to release your modifications under the GPL.
On the other hand, the GPL offers some freedoms:
If you're just an end user of a GPL-licensed product, you aren't required to distribute it.
You can still charge money for your product, even if it's released under the GPL.
Your product doesn't have to become a "GNU" product, and you don't give up your copyrights under the GPL.
Here are some more resources for learning more about the GPL and other non-restrictive public licenses: