ARK provides a systematic way for sysadmins to describe and share their solutions to sysadmin problems; i.e., to encode the "added value" they have provided over and above vendor-supplied computing equipment.
With ARK, you can compose new sysadmin "added value" from other ARK-systematically-described solutions; for example, "We want our team's Apache installation to be the same as Team Y's, except for this part, which we want to do differently."
With the ARK framework, all of your sysadmin "added value" -- whether about packages, users, printers, license agreements, etc... -- can be expressed in a uniform way.

Everything else is just details :-)

Our essential tool is the ARK configuration language. But first, be sure you understand the ARK ``object ideas''.

And an alternative basic description...: Steve Traugott, of Infrastructures fame, summarizes ARK this way:

ARK is an extensible language for precisely expressing systems administration tasks, methodologies, and habits. The language is written in XML syntax, and is optimized for collaborative code sharing of subsidiary modules (typically Bourne shell or Python scripts). There is an interpreter currently available, written in Python, also named ark.
[This] web site includes example code, written in ARK, for doing systems administration using various administration teams' policies and procedures. These examples can be combined with your own, or any other, team's code to create a description of your own unique site, its processes, and procedures.
Actions described in the ARK language need not be limited to direct manipulation of machines: the language is intended to be flexible enough to assist with other systems administration tasks, such as equipment orders or trouble tickets.
[This] web site includes a simple demonstration of ARK, showing how ARK and some of the example code can be used to drive builds of generic GNU packages. See http://ark.sourceforge.net/try-ark1.html.