The most basic article level metrics are the number of publications and the times the article(s) has been cited. That is, how many times an article has appeared in the reference list of other articles, books, etc. The times cited are heavily influenced by the underlying publications covered in the database where the citation counts are obtained. Consequently, you will often obtain a different number of citation counts from different sources (e.g., Web of Science, Google Scholar, Dimensions, etc.). There are also significant differences within and among disciplines in publication and citation behavior.
Knowing an article has been cited X times has little meaning by itself. It is best to supplement the absolute number of times cited using ratios or percentiles to normalize and provide context. Available normalized metrics include: field citation ratio (FCR) in Dimensions, relative citation ratio (RCR) and NIH percentile in iCite, citation percentiles in Web of Science via the Author Impact Beamplot, and citation percentiles in the Essential Science Indicators.
Additional article level metrics include various altmetrics such as downloads/views, citations in policy documents, citations in patents, mentions by various media outlets, etc. See the Altmetrics tab for additional details, though Altmeterics.com [i.e., Altmetric Explorer] and the journal publisher's website are often the main sources for these types of article-level metrics.
Scholars@TAMU, Texas A&M University's researcher profile system, aggregates many of these metrics for you in one place! See About Scholars@TAMU for more information.