Move to the directory where the module’s source file was unpacked, and then:
% /path/to/apache/ bin/apxs -cia module.c
In the case of a third-party module that consists of a single .c file, there is a good chance that it can be built and installed using the Solution. Modules that involve multiple source files should provide their own installation instructions.
The -cia options mean to compile, install, and activate. The first is pretty straightforward; install means put the .so file in the place Apache expects to find it, and activate means to add the module to the httpd.conf file.