You can here find pre-compiled builds of the chemfiles library for a variety of platforms (operating system & CPU architecture). Pick the one you need and extract the archive to install.
The chemfiles-static archives contains a static library build of chemfiles, the header files for the C and C++ interface to the library and the CMake configuration to import the library in your own project.
The chemfiles-shared archives contains a shared library build of chemfiles the header files for the C and C++ interface to the library and the CMake configuration to import the library in your own project.