Let's call the directory in which you installed the Giggle header files includedir. For example, if the file giggle.hxx was copied into /usr/local/include/CyberTiggyr/giggle/9.1, then includedir is /usr/local/include.
Let's call the directory in which you installed the Giggle link library libdir. For example, if libgiggle-m.n.a was installed into /usr/local/lib, then libdir is /usr/local/lib.
In your Makefile (or equivalent), you'll need to tell your C++ compiler about includedir so that your C++ programs can #includeCyberTiggyr/giggle/giggle.hxx. For most C++ compilers on Unix, that's done with the -Iincludedir command line option.
You'll also need to tell your compiler at the link phase where to find the Giggle link library. For most Unix compilers, that's done with the -Llibdir command line option. You'll also have to tell your compiler or linker that it needs to search for the Giggle link library. That's usually done with the -lgiggle command line option to get the most recent installation of Giggle, or with the -lgiggle-m.n to get a specific version of Giggle.9.2