Pip4Blender is installed exactly like any other Blender add-on, and is distributed as a single Python file.
From the User Preferences panel, select ‘Install Addon from File’, and select the pip4blender.py file.
Installing Pip in the Blender environment is also required before the rest of the functionality of the add-on is accessed. This can be done by selecting the ‘Install Pip in Blender’ button, but only needs to be done once for any given Blender installation.
This might take a few minutes to run, if you want to watch the installation progress you should run Blender from a terminal.