Right near the top of `tar --help`:

    tar -xf archive.tar  # Extract all files from archive.tar.

If you work with lots of different types of archives or have a hard time remembering the various tools and arguments, I recommend dtrx (Do The Right Extraction). Super simple and it ensures you don't accidentally dump a whole directory tree somewhere it shouldn't. Assuming you have pip and hg installed, you can install the latest version to your user site with the following command:

    pip2 install --user hg+http://www.brettcsmith.org/2007/dtrx/dtrx

Then all you have to remember is `dtrx ARCHIVE...`