The following documentation shows the process of installing and authorizing ArcGIS Desktop software. Authorization instructions start at step 11. Download the software here. Also download the .prvc file for authorizing the software here (This is a plain text file. You can download it either by right-clicking on the link above and choosing "Save Link As", or simply click on the link, so that its plain text contents are visible, and then choose "Save" or "Save As" from your browser's File menu).
Click I accept the license agreement and then click Next.
Choose Complete under the installation type and click Next.
Click Finish and the ArcGIS Desktop software will be installed.
Under Select a product chose Advanced (ArcInfo) Single Use. Then click Authorize Now.
Click I have received an authorization file from Esri and am now ready to finish the authorization process and then click Browse to find the .prvc file you downloaded earlier.
Click Authorize with Esri now using the Internet and then Next.
Chose whether or not you want to authorize any exentions and click Next
If you would like to try an evaluation copy of one of the extensions you can chose so here. Then click Next.
Click Finish. You have now successfully installed and authorized ArcGIS.
*Note: Although the Provisioning File includes authorization numbers for various extensions, these extensions are not automatically enabled. Please see the next step to learn how to enable these extensions.
Enable extentions by selecting Extensions... from the Customize drop-down menu.
Check the box next to the name of the extensions you wish to use, then click Close.