A lot of useful information concerning Apache is available. Please review these sources, especially the official Apache website and the mod_ssl website.
http://httpd.apache.org — The official website for the Apache Web server with documentation on all the directives and default modules.
http://www.modssl.org — The official website for mod_ssl.
http://www.apacheweek.com — Published weekly online and distributed via email to over 12,000 people world-wide, Red Hat's Apache Week is the definitive online resource for all users of Apache and Apache-based Web servers. Apache Week covers in-depth features and provides simple tutorials and HOWTO's for novice and expert users alike.
Apache Desktop Reference by Ralf S. Engelschall; Addison Wesley
Written by ASF member and mod_ssl author Ralf Engelschall, the Apache Desktop Reference provides a concise but comprehensive reference guide to using Apache at compilation, configuration, and run time. This book is also available for you to download online at http://www.apacheref.com/.
Professional Apache by Peter Wainwright; Wrox Press Ltd
Professional Apache is one of the many books in Wrox Press Ltd's "Programmer to Programmer" series, aimed at experienced Apache users and Web server administrators who are using Apache for the first time.
Administering Apache by Mark Allan Arnold; Osborne Media Group
This book is targetted at Internet Service Providers who aim to provide more secure services, Web developers, applications programmers, right up to the corporate system administrator.
Apache Server Unleashed by Richard Bowen, et al; SAMS BOOKS
Rich Bowen and Ken Coar's book aspires to be the definitive encyclopedic source for Apache.
Apache Pocket Reference by Andrew Ford, Gigi Estabrook; O'Reilly
Apache Pocket Reference by Andrew Ford is the latest addition to the O'Reilly Pocket Reference series with sixteen other titles to its name. On its back cover, O'Reilly markets the Apache Pocket Reference as a companion volume to Writing Apache Modules with Perl and C and Apache: The Definitive Guide, 2nd Edition.