There is a zip/unzip option in the context menu so is it accessible from the command line?
Yes and no.
rundll32.exe zipfldr.dll,RouteTheCall filename.zip
would open the file in the explorer as a "compressed folder" similar to clicking open a zip folder
There is no other entry point in zipfldr.dll that allows decompressing files directly from command line. I would suggest using the 7zip command utilities or unzip.exe as these are free (as in freedom as well as in beer)
If you already have Java JDK on your PC, and the bin directory is in your path (in most cases), you can use the command line:
C:\Program Files\Java\jdk1.7.0_45\bin>jar xf test.zip
Complete set of options for the jar tool available here.
Extract jar file
jar x[v]f jarfile [inputfiles] [-Joption] jar x[v] [inputfiles] [-Joption]
If you don't have JDK installed I would recommend installing 7-Zip, since it's very lightweight: http://www.7-zip.org/
As Jason Duffett's reply
you can try "expand MyFile.zip myFile" in cmd line
No it doesn't by default, but check here to do it anyway: http://stahlworks.com/dev/index.php?tool=zipunzip