To get started, you can browse the top 100 publications in several languages, ordered by their five-year h-index and h-median metrics. To see which articles in a publication were cited the most and who cited them, click on its h-index number to view the articles as well as the citations underlying the metrics.
For a quick overview of general Google Scholar limitations, see those listed for Google Books and Google Scholar. Many of these problems are applicable to this tool.
For good reviews specific to Scholar Metrics (the evolving story), see:
Google Scholar Metrics: An Unreliable Tool for Assessing Scientific Journals
(Delgado-López-Cózar, Emilio; Cabezas-Clavijo, Álvaro. El profesional de la información, 2012, July-August, v. 21, n. 4, pp. 419-427)
Google Scholar Metrics Updated: Now it Begins to Get Serious
(Delgado López-Cózar, Emilio; Cabezas-Clavijo, Álvaro. EC3 Working Papers, 8; November, 16th, 2012.)