Can someone please explain the usefulness of Flash?

Hi, I’m hoping for someone to help me understand the usefulness of Flash. I have been trying to choose between the iPad 2 and a Galaxy Tab 10.1. A light-weight actual notebook is also an option. I would like to know whether I’d truly be missing anything if I don’t have Flash on the iPad 2? There’s another thing that I’m ignorant about. Is it mandatory to use an a site/company’s app or can I simply browse the webpage. For instance, I can either choose a bank application or visit the respective webpage for online banking. Which one will be preferable? Also, how do PCs and notebooks differ from each other actually? I know about some of the software, like MS Word, Excel and so on, but can you please tell about anything else? Your help would be highly appreciated. Thanks a lot for your time.
