From the Eclipse download page obtain your operating system's version of Eclipse IDE for Java EE Developers. Juno is the most recent Eclipse version as the time of this writing, but if you already have the previous Helios or Indigo versions of Eclipse on your machine that should work fine as well. After extracting the application, double-clicking the Eclipse icon located in the Eclipse root directory should bring up the IDE; note your specific operating system's version may provide additional convenient options (menu items, desktop icons) for activating Eclipse.
After installing, have Eclipse point to the JDK you downloaded in the previous step. This can be done by selecting menu item: Windows | Preferences and the corresponding Preferences Dialog, selecting Java | Installed JREs from the left-side menu tree.