How to create a URL for an image?

You mean you are trying to upload an image to a website, but that website is asking for a URL for your image?

That means you first need to upload your image to the internet, because if I understand correctly, your image is currently on your computer.

To upload your image to the internet and get a URL that points to it, go to http://imageshack.us, click on browse, choose your image, and then click on host it!

Then it will show you a page with your image small and at the bottom of that page, you will find an address with "Direct link to image" written on the right:

this address is the URL of your image.