When it asks me my url address when uploading a pic, what is that?

Sorry, they say it better than I can so here it is WWW FAQs: What is a URL? (http://www.boutell.com/newfaq/definitions/url.html)

Just to give a summary(ish) version of what it is. A URL (Uniform Resource Locator) is the "name" you use to access a website. Basically it is what line the will appear in your address bar in your browser (usually along the top). URL's are used as they are a easy system for humans to remember. All websites/servers and accessed by IP address (200.85.64.12 for example), however IP address can be heard to remember so instead we assign a URL to a site and then make a entry in a server called a DNS (Domain Name System) server. When you enter a URL into your address bar, (or click a link to one), for example Google (http://www.google.com) your computer sends a message to the DNS server to find out http://www.google.com's IP address so it can access it.

All URL's start with the prefix http:// as this defines that you are using the Hyper-Text-Transfer-Protcol which is what websites use. URL's with also have a suffix for example .com, co.uk, org. etc etc. After the suffix will usually be a slash the is a path to a specific file on a server. For example the comupting section of Ask Me Help Desk has a address of https://www.askmehelpdesk.com/computers-beginners

Broken down we have first http://, defing that Hyper-Text-Transfer-Protcol is used. The www. Which defines the servers system (does not have to be www for website use though). Next we have the .com part which is called a TLD (Top Level Domain), and the need/use for it and really immaterial at this stage in explaining URL's. Lastly we have the /computers-beginners which is the "path" on AskMeHelpDesk's webserver the computing section.

So if you need the URL of a image find the image you are looking for. Then in most browsers you can right click and select "Open Image" at this stage you should get a white screen with image in the centre and what is currently in the address bar is the URL you need.

Should be something like http://www.website.com/images/imagename.jpeg

Note: Some browsers such as Opear allow you to right click an image and instantly select "Copy Image Address" which will just copy the direct address to your clipboard for you.