ITIL is about people. In fact, ITIL starts with a commitment to the people of IT, because it consists of a series of individual IT practitioner certifications. These certifications help improve the skills required to deliver high quality, repeatable, and well-controlled IT services. There is no "company-wide ITIL certification"- these would, in fact, be handled by the international standards organization ISO via ISO 9001/8 and 20000 corporate certifications.
Second, ITIL is about process. There are different approaches to process implementation based on which "version" of ITIL you are inclined to adopt. But without debating the merits of ITIL "versions," let us presume that any ITIL implementation discussion ultimately has roots in the principle of Process Improvement. Besides, ITIL v2 and v3 are more alike than different at a fundamental level. Both embody essential ITSM processes that every IT organization must perform to the best of its ability-you're doing them as a matter of course whether you have efficient processes in place, or not. Thus almost any question you might ask about ITIL comes down to this: how do you best make use of whatever essential ITIL v2 and/or v3 elements make sense for you to adopt given your specific needs.
Third, ITIL has starting points. This is one of the most widely discussed topics as of late, especially as ITIL isn't considered to be highly prescriptive. Rather, it's a set of "good practice" guidance for IT practitioners to follow. They may adhere to these strictly, as outlined in each of the books. Or, more likely, practitioners may adapt the ITIL guidance as they see fit based on the unique skill sets, goals, and functions of their unique IT organization.