What you need is:
oUF core:
http://www.wowinterface.com/downloads/info9994-oUF.html
An oUF layout:
Choose one you like from here:
http://www.wowinterface.com/downloads/cat127.html
You need a layout in order so use the functionality provided by oUF.
The supported oUF plugins by your chosen layout are normally listed on the layout's page.
Some layouts have plugins and even oUF's core embedded, meaning you don't have to install them separately. That's normally mentioned on the layout's page.
oUF's core, the layouts and the plugins are normal addons. You install them separately in <your wow folder>\Interface\AddOns.
Beware: layouts do not have to support every available plugin out there and not even every possible feature of oUF. Some don't provide all unit frames (raid frames are a common example). Most of them don't have any graphical setup like PB4, so you need at least some basic LUA knowledge to tweak stuff to your liking. Most layouts lack character specific options, meaning you'll end having the same looks and functionality for all your toons.
If you need specific support, you'll have to provide more information: chosen layout, LUA errors etc.