NB these files are quite big and contain no source code so it's a bad idea to use git to clone this repository. Use the download zip option
Unzip the 32 bit or 64 bit dll files into the main directory of your python project that's using pi3d.
If your python is 32 bit you need to use the 32 bit dlls and 64 bit for 64 bit python. You can tell the type of python when you first open an interactive shell.
i.e. if you downloaded the github pi3d_demos repository to
C:\Users\another\Documents\GitHub\pi3d_demos-master
then that's where you would put the three dlls in order to be able to run the demos.
See general instructions here:
http://pi3d.github.io/html/ReadMe.html#windows
This zip download will be about 5.6MB
NB as a general rule you should ensure that your virus checker gets a sniff at all .exe and .dll files, including these. I assume they're clean but I basically just downloaded and compiled the ANGLE project code from