Go to the AcademicSoftware page for GeoGebra. Choose whether you want to download and install GeoGebra, or prefer to use the online version.
For the ONLINE version:
Step 1: Click the green button 'GeoGebra Classic 6 Online' on the right. You can get started right away.
To DOWNLOAD and INSTALL:
Step 1: Under 'Select version' at the top right of the page, choose 'GeoGebra 6'
Step 2: Click the green button ‘Download GeoGebra'
Step 3: The installer file will be downloaded. Run this file.
Step 4: GeoGebra will start and you can start using it right away. You can choose to remove the installer file and run the program from the Start menu.