While museum wall labels are fairly transparent, there are a few quirks to understand. The example below is representative of a typical label, but museums do vary their formats.
Artist’s Name (with Country of Origin, Birth and Death Dates in parentheses)
Title of Work of Art [almost always italicized]
Medium [i.e. what its made of], dimensions [usually L x W x H]
How the museum acquired the object [donation/gift, purchase, loan, etc.], sometimes the year
####.### [Accession number, oftentimes the year the work was acquired and the number it was that year. 2009.2 means the object was acquired in 2009 and was the 2nd object acquired that year]
On many labels, there is a paragraph of information written by the curators or more rarely the educators pointing out interesting information about the object itself, the artist, the method of the work's creation, or the country or time period in which it was created. Some labels omit this section all together, frequently in contemporary galleries. The best labels don't use jargon without defining terms or refer to anything you can't see (i.e. other works, other artists).
Want to impress your friends? Position yourself in front of the label and casually glance at it while talking (docents and lecturer use this trick-of-the-trade all the time). If you are talking with childre, sometimes it's best to hide the label so those kids (who always have great eyes) don't just read you what the curators wrote--sometimes just knowing the title can skew their perceptions of the work.