Question: What does [it] mean by blog rank PR 1/ 2 / 3 etc ?
A “PR” ranking is short for a Google Page Rank.
Simply put, the Google Page Rank is a number from 0-10 on how “popular” google considers your site. The term popular is a misnomer really, because the actual calculations google uses to compute your PageRank include links in from different sites, number of pages index, and more.
A good place to check your Google Page Rank is http://www.prchecker.info.
A more thorough explanation of the PageRank history can be found on Wikipedia at http://en.wikipedia.org/wiki/PageRank,
Sorry for the short answer, but all the information you need can really be found on wikipedia, and with formulas and a lot more information.