The program is distributed as a compressed tarfile. After downloading it to your disk and placing it in the directory where you would like to create the Coxeter directory, it is enough to say tar xzf name_of_compressed_tarfile, to create the directory coxeter_3.0_beta3, which contains the full source code of the program, and some additional information. Then, it should be enough to descend into this directory, and say make, to obtain the executable coxeter. To run the program, simply type coxeter, or ./coxeter if your path doesn't have . in it.
The makefile calls the g++ compiler by default; if this is not available on your system, you should edit the makefile and replace it by the C++ compiler that you have. I will be happy (or at least interested ...) to hear how the program fares with other compilers---but unfortunately I cannot promise any help with compilation problems (unless they originate from obvious bugs in the program.) The program has successfully compiled and run in the following environments:
The installation instructions so far have assumed that we were installing the program in a user's private directory. This is mandatory if one wants to add personal extensions to the program, which require recompilation. If this is not the case, then the program may be installed in /usr/local, for instance. However, it will then be necessary to edit the directories.h file, to add the appropriate prefixes (for instance /usr/local/coxeter_3.0_beta3/) to the directory-paths COXMATRIX_DIR, MESSAGES_DIR and HEADERS_DIR, or the program will fail to find the help messages and header files which it needs.