A library is a set of code already written and packaged, which you add to your project to drive a component or a protocol through a simple interface, without rewriting the low-level code yourself.
What is it for
Getting an I2C sensor to talk, printing text on an OLED display or driving a stepper motor calls for driver code that is often long and delicate (registers, timings, protocol). A library wraps that work up: you call display.print("...") or capteur.lire() without knowing the detail of the component. It is the same principle of reuse as the modules of a language, applied to hardware. It is also the normal way to use a Shield: every add-on board comes with its own library, which exposes its functions.
Installing and choosing
Most IDEs include a library manager that downloads them and keeps them up to date in a few clicks (see IDE). Three habits of caution: check that the library is maintained (recent commits) and compatible with the target board (a library written for an Arduino Uno does not always work on an ESP32), and freeze its version on a team project so that an update does not change the behaviour halfway through. Putting it to work step by step: Using a library for Arduino, Using a library for MicroPython.
See also
- IDE — where libraries are installed from
- Shield — the add-on board and its associated library
- Arduino — libraries — installing and using a library in practice
- MicroPython — libraries — the same method for MicroPython
- Microcontroller — the target that runs the code