I am extremely mechanically minded. What is in a library (not counting the mbed library)? .cpp and .h files? libraries? When a library is included, is the inclusion process simply copying in the code contained in the library, as though it were an include file?

Thanks for giving my earlier question your attention!

Sorry the delay - "what is in a library?" Typically, you would find a collection of functions that are reusable. For example, if you had a temp sensor that produces a voltage, you would create code to read the analog input, and perhaps linearize the voltage reading to a temperature and scale it to degrees C (or F). You could put this in "main", but you might also create a function "ReadTemperator()". If you put this function into a separate file and compile it as a library, you can reuse this [presumably tested and trusted] library in many different programs. You don't need to worry about how it works anymore, you just have defined a standardized way to get the temperature. So, to put it into a [possibly poor] analogy, the library is composed of components - like a transmission, which is pretty useless as a component until you attach it to a power source (engine), and in turn deliver the power (to the axle to turn the wheels). The transmission (aka library) could be quite a complex component, but the interface is defined, so again, you don't have to deal too much with the internals.

How to use a library? If we go back to the simple example, the code might be one .cpp file and the declaration for how to use the library would be exposed in a single .h file. The .h could have a very simple line like:

float ReadTemperature(void);

If you put that .cpp and the .h into a new folder, then you can convert that folder into a library.

To make the library more useful, you might put some additional documentation into the .h file.

/// Read the temperature sensor and return the value in degrees C.
///
/// This reads the temperature sensor (using part # AB12345) which is wired to 
/// Analog Input channel 2. It then takes the non-linear output of that sensor and
/// linearizes it to within 0.5 degrees over the range of -10 to +50 C.
/// It will function over a wider range of -40 to +85C to within 2 degrees C.
/// 
/// @returns single precision floating point value representing the temperature
///               in degrees C.
///
float ReadTemperature(void);

The subtle formatting shown here is "doxygen" formatting, so building the documentation creates an easier to read aid to this library.

Finally, to use this library, your program would have something like this:

#include "TempSensorAB12345.h"

...

float tempC = ReadTemperature();

if (tempC > 95.0f) 
    printf("Alert: Temperature (%3.1f) exceeded alert level (95.0)\r\n", tempC);

One last pass - back to the "transmission" example, the library can be quite complex and do a lot. It would be a good practice not to put unrelated functions into a single library, but to create additionally libraries. So, if I want to display the temperature, I could create some functions to control a display, and I could put those functions into the temperature sensor library, but that would not be a best-practice. Instead, Create a separate library for the display.