The micro:bit is a low cost microcontroller board developed by the BBC and a range of partners. You write programs to make things happen with the micro:bit.
You have a choice of languages and can program online at http://www.microbit.org. There are also some offline solutions for Python and C++.
You can also connect a whole host of electronic components to create all sorts of contraptions or just to learn how to make them work.
Click on the headings on the right of the page to see the links for each subsection. There are well over a hundred pages here, with ideas, examples and challenges to get you started with the micro:bit.