The Umbra plugin is distributed as a UE4 plugin that lives in the Engine\Plugins\Umbra directory. The plugin is built as part of the UE4 engine build.
In addition to the plugin, a standard Umbra 3 release package for the applicable platforms needs to be present in Engine\Source\ThirdParty\Umbra.
The Umbra UE4 integration package contains both of above, simply extract the provided archive in your UE4 root directory.
You can optionally regenerate Visual studio project files to include the Umbra plugin in your visual studio solution.
UE4 Engine patches
At the time of writing (version QA build 12/2013) a number of source code patches need to be applied to Engine code for the plugin to build and function properly. These patches are provided as a series of .patch files in the root directory of the Umbra UE4 integration archive.
Review and apply these patches in numerial order, for example:
patch -p0 < 0001-first-patch-description.patch
patch -p0 < 0002-second-patch-description.patch
The need for these patches is temporary, ultimately the Umbra plugin is expected to work against unmodified UE4.
The Umbra plugin is enabled for your project by adding an entry in the appropriate game .ini file, under the "Plugins" section:
Additionally to be able to compute Umbra data in the editor you will need to have an active Umbra 3 license key configured. The plugin inspects the "LicenseKey" entry in section "Umbra" of the editor .ini file:
Alternatively you can place the "umbra_license.txt" file in the engine binaries folder.