Piper's first part, "The Basics," goes over financial literacy terminology and concepts:
Stock v bonds v funds,
401k and Traditional (pre-tax deposit, taxed withdrawal) v Roth IRA's (after-tax deposit, untaxed withdrawal),
and basics of budgeting, risk and inflation.
In part two, Piper echoes many of the ideas put forth by other personal finance experts. Only trade funds, you are not smart enough to know which exact stocks to pick, and in all likelihood, no one on earth is ('successful' fund managers with past success are just as likely to have simply gotten lucky several years in a row).
A wise investor should go with index funds, as they have consistent returns, low fees and little portfolio turnover which minimizes taxes.
If low-cost index funds aren't available within one's 401k plan, prioritize the lowest expense ratio and portfolio turnover options.
For asset allocation, Piper offers a bond to stock fund rule, where bond percentage is equal to age. You can differ from this depending on your volatility tolerance (this may be psychological, or even longevity based, as those who live longer have more time for volatility to average out), my family, for example, would consider this extremely conservative. Somewhere between 20 - 40 % of stocks should be international. As a side note, John Bogle recommends less than 20%, but consensus seems to be one Piper's side.
Intervals between 'rebalances' to maintain or adjust asset allocation should be on a timeframe longer than one year. You also shouldn't really be checking on your funds more often than that, as seeing dips or hikes can make staying the course difficult.
In the third and final part, Piper again emphasizes staying the course, not peeking, and not responding to bear and bull markets. He gives some advice on seeking out good financial advisors with strong fiduciary responsibility. Piper ends on a few sections recommending automated investing techniques and urges the reader to steer clear of newsletters and media sensationalism more broadly.