This is, basically, a short primer on rhetorics: how to come off best in arguments, irrespective of whether you are right or wrong. In fact, despite being close to 200 years old, it would quite happily fit into the "Idiot's Guide" series: it is concise, understandable, witty and of great practical use.
In some respects, this book reads a bit like "The Art of War". It is a catalogue of 38 rhetorical "dirty tricks", which include diversion, obfuscation, over-generalisation, mis-categorisation, false syllogism, personal attack etc., with short explanations (from a couple of sentences to 3-4 pages) and illustrative examples. It's all very easy to absorb, and you can easily finish the whole thing in a couple of hours.
There is some argument over whether this book was intended as an out-and-out satire. Undoubtedly, having a dig at the academic establishment was one of the things on Schopenhauer's mind, and much of the book is tongue-in-cheek. This does not make it any less useful. The underlying theme is dead serious: if you cannot recognise and counter-act sophistry and demagoguery, you will end up getting bamboozled into accepting and maybe even endorsing logically unsound arguments - at best losing face, at worst getting conned. This stuff should be taught in schools!