What is a license and how may I use code under a license?

Question

(Let me edit this question to try to better get across what I am asking.)

I don't understand what a license is and how I may "use" it. From the little that I do understand, there are two situations:

1. One writes a program/source code and puts a license on it. The license says how other people may (are allowed) to use the program/source code.
2. I find a program/source code and would like to use it. The program comes with a license and the license tells me how I am allowed to use the program/source code.

It is this second point that I am confused about. I have no experience with "using" licenses. I see some previous questions about licenses being closed, so just to make it clear: I am not asking for legal advice. I just want to make sure that I am doing it "right". I just want to know how one can use a license.

To given a concrete real world example of what I am asking:

I want to use the library CryptoJS 3.1 to make a web page (to put online for the whole world to see) using this library, but I am uncertain about how I may do this.

From what I understand: according to the page about the library, the the library is offered under a license called the New BSD License.

But I don't understand what this license is telling me about how I am allowed to use the source code. Specifically, I would appreciate if someone could explain (as if I was a 12 year old):

What do I need to do to use this library on my web page?

For example: Do I need to give tribute with a link or something like that?

One specific thing that is confusing me is that on the page of CryptoJS 3.1 it actually doesn't tell me what the license is verbatim. It says that the license is the New BSD license. There is a link to this page. And one that page is a template for a license.

So how do I make sense of this?

In summary: I would like to use CryptoJS 3.1, but I don't know how I may do that.

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(I have figured out the export regulations requirement, so that isn't an issue for me.)

Answer 1

In order to use CryptoJS, you must follow the terms of its license. Which means that you can either use the js files directly from http://crypto-js.googlecode.com as shown in their examples, save those files locally and distribute them yourself from your own server, save those files locally and make any sort of adjustment you want to them, or even compile your JavaScript to an executable or obfuscate your entire project to your heart's content.

What you CANNOT do, however, is remove the copyright license from the start of each JS file, or violate any of the rest of the terms at the license URL linked therein.

http://code.google.com/p/crypto-js/wiki/License

Assuming that you just want to make a website and include direct links as shown in the cryto-js examples, you don't need to do ANYTHING else.

(Whether or not you could use someone's js file via direct linking without their permission is an entirely different question, and not what you're asking here.)

Again, YOU DO NOT NEED TO RE-LICENSE YOUR CODE. Either your website in part or in whole or any modifications that you make to Crypto-JS. So long as you preserve their copyright notice and liability disclaimer, you can do whatever you want with it.

Answer 2

You just have to post the source code if you make any changes, but it is free to use.