NVDA can be downloaded from the site: nvda-project.org, please consider donating if you do use the software much, it is invaluable to users and developers, and is far cheaper than other Windows screen readers.
NVDA works best with Firefox, and also supports Internet Explorer.
Most NVDA-specific keyboard commands usually consist of pressing a particular key called the NVDA modifier key (INS by default), in conjunction with one or more other keys.
You can use the preferences (i.e. INS-n) to change to a laptop layout, which affects a few of the combinations below.
This page uses NVDA as the generic command, so by default NVDA = INS.
Windows basic keyboard commands (like tab and enter) work as normal, NVDA commands work on top of those.
These keys can be used in browse mode, and pressing shift modifies it to go backwards.
E.g. h goes to next heading, shift-h goes to the previous one.
For more, please see the full user guide on http://nvda-project.org/