VoiceOver is part of iOS, no installation required. To enable VoiceOver go to the Settings > General > Accessibility > VoiceOver.
I set it to toggle on/off when triple-clicking the home button. Just remember that is how it works, in case you turn it on by accident in future!
Using VoiceOver completely changes the touch interactions, if you aren't ready it will be completely unusable.
It is worth trying the VoiceOver practice which is available in the settings area.
There are two main navigation styles you can use across iOS including websites:
You can flick right & left for next & previous, and double-tap to select.
You can put one finger down and drag it across the surface, VoiceOver will read out whatever is underneath your finger. To select something you tap another finger anywhere else on the screen.
This feature enables you to select elements like headings, links, containers, lines, words and characters.
Put two fingers on the screen and twist them around, like turning a disc, until you get the headings option.
I find this really useful for skimming by heading (flick down) and then reading from there: flicking right for next, or a two-finger flick down to read all.
This is also useful for forms, if you select that option when in a set of controls.
For more, please see the full iPad user guide (16MB PDF), from page 100. (http://manuals.info.apple.com/en_US/iPad_User_Guide.pdf)