I cannot find the guide to get started with using HarfBuzz in my own app.
I looked here:
http://freedesktop.org/wiki/Software/HarfBuzz/
This seems to be the official page of HarfBuzz.
I looked over Download, Building and Development sections. But I must be overlooking something.
Some good and simple examples are listed on Harfbuzz wiki, 1, 2
I suggest you a higher level library, Pango if you need layout things like line wrap and I guess you would find better doucmentation for it than HarfBuzz itself.
You may have a look at State of Text Rendering also.
I was facing the same issue and was looking for the instructions. Finally I found at below link. It includes Android sample app with build instructions and all. Enjoy :
Indic-text-renderer
I found harfbuzz html docs here
http://fossies.org/linux/harfbuzz/docs/html/index.html
I've managed to find a post to the harfbuzz mailing list with some (non working) example code here; however, it's from 2008.
It also looks like the source code itself contains some documentation, although I think it needs to be generated via the makefile.