License requirements for commercial program

Answer 1

This will usually mean that if you build a patch or other modification of the program and want to distribute it you must also publish the sources of that modification under a license explicitly mentioned in the program license text.

In some license types this includes both the other program and any program using that (including your program). In others (like LGPL) this will only be required only for modification made to that program, but not to your program if they are separated (LGPL is typically used for libraries and doesn't enforce publishing the library consumers).

Answer 2

simply:

you can sell (and release with your own commercial license) your own app built with the provided code.

but:

you can not improve on the code (of the software you are using within your app) directly and not give it to public domain (usually it is in the original license of the software).

Answer 3

Instead of relying on those summaries, you would be advised to carefully read the license for any open source license you plan to use in a closed source product.

For instance, LGPL does not actually require you to release source code changes to the public domain. Rather, it requires you to release them under the terms of the LGPL.

If you are nor sure that you understand the implications of a particular license, talk to your company's lawyers.