From Wikipedia -

PageRank is a link analysis algorithm that assigns a numerical weighting to each element of a hyperlinked set of documents, such as the World Wide Web, with the purpose of “measuring” its relative importance within the set.

The algorithm may be applied to any collection of entities with reciprocal quotations and references. The numerical weight that it assigns to any given element E is also called the PageRank of E and denoted by PR(E).

It's the basis of how Google works, so yes, it's very important. However, it's nothing you should worry about or change, so don't lose sleep over it.

Do all the right things, and add relevant content regularly in a well optimized environment, and the link (and PageRank) will come.,