There are plenty of places to get more on the basics on GDP. Here are a few of them:
The Bureau of Economic Analysis. The BEA, which puts out GDP statistics regularly, is a great place to go for the basics. The latest GDP news release can be found here, and there are also a wealth of other documents: a guide to the National Income and Product Accounts, a look at the methodology of counting GDP, and a rundown of GDP by industry, complete with an explanation of how GDP and gross output differ.
International data. Want to know how the US economy stacks up against other countries? Check out data from the World Bank, IMF, and OECD.
Information on a no-growth economy. It’s a fringe idea, but some people think it would be possible to have an economy in which there is no growth. See the basics at the Center for the Advancement of a Steady State Economy.