The micro:bit is a microcontroller, also called a mini-computer. It has inputs, outputs, a processor and storage. You can code with Blocks, JavaScript, Python, C++, Scratch, and more. You can access the Blocks and JavaScript editors using makecode.microbit.org, you can access the Python editor at python.microbit.org, and you can access the C++ editor using developer.mbed.org.
See the Quick Start Guide