You want to add SSL support to your Apache server with the mod_ssl secure HTTP module.
The mod_ssl package requires source-level changes to the base Apache code, and so the version of the mod_ssl package you install must match the version of the Apache distribution you have. If your Apache installation doesn't include the source (such as if you installed a binary-only RPM or other vendor distribution), you won't be able to add mod_ssl to it.
In addition to the Apache source, mod_ssl requires that you have Perl and the OpenSSL libraries installed. The with-ssl option on the build configuration statement indicates where this is located; if it is in a vendor distributed directory, the special keyword SYSTEM tells the build to look for it, and you don't have to find it yourself.
Unlike most other Apache modules, when adding mod_ssl you run the ./configure script that's in mod_ssl's directory rather than the one in the Apache source directory; the module's script makes changes to Apache's and then invokes it directly.
This recipe is the bare basics; there are many optional components and features that mod_ssl allows you to specify at configuration time. For more information, consult the README and INSTALL files in the mod_ssl source directory, or the mod_ssl web site at http://www.modssl.org/.