The simplest web pages are made up of just text plus some coding to tell your browser how to display them.
Slightly more complex pages may have graphics and other design elements to make the page more attractive and the site, as a whole, easier to navigate. They may also have audio and video clips.
To understand how they're used you need to know that your browser (a ’client’) interacts with a distant computer (a web server) to show you web pages, and that the web server itself also runs many programs that are used (’called’) when they're needed.
So, for example, when you enter your personal information into an address form, that information will be fed into a database program running on the server's end of the connection that will store it, retrieve it when needed, and feed it into other programs – for example, one that sends that information to your credit card company for authorisation.
On the other hand, Java is three things. Firstly, it's a programming language. Secondly, it's a ’virtual machine’ - a program (’run-time environment’) you can install on any computer (including mobile phones) that can run any programs written in Java. Those programs will be safely ring-fenced (‘sandboxed’) so that nothing they do can affect the working of the rest of your computer.
Most people will find that Java has been installed on their computers whether they were aware of it or not. Java was designed with security in mind, but all software has potential security risks, especially when (like Java) it is running programs written by unknown entities across the web. You should make sure you keep Java regularly updated to minimise the risks.
Internet Explorer for Windows
Go to the 'Tools' menu and choose 'Internet Options'.
Next, click the 'Security' tab. Make sure the 'Internet Zone' is highlighted and press the 'Custom Level' button to open the security options.
Look for the entry near the bottom of the list which says 'Scripting', then 'Active Scripting' and make sure it is enabled.
Safari for Mac
Go to the Safari menu and choose 'Preferences'.
Firefox users should go to the 'Tools' menu and select 'Options'.