I don't know why I've waited so long to do this. I love messing around with home automation, and here's a fully-functional computer with wireless and 20-odd GPIO (input-ouput) pins.
I've also been meaning to begin using Linux (technically I already do, I use MacOS's Terminal a lot, and have set up and run a couple of Ubuntu servers with python and mysql). The Pi has a desktop, USBs for keyboard and mouse, HDMI output. This one has 1Ghz processor 256Mb of ram and for a HD, whatever free space is on the card that you put in. All of this on a board which is half the size of a credit card and costs less than a tenner (or less than a fiver for the non-wireless version).
When we finally invent time travel, or at least find a way to communicate across time (as per Gibson's The Peripheral which I heartily recommend) my teenage self will be astounded by this information. I remember the day when I first heard the word 'megabyte'. It wasn't far off the day that I felt very powerful after plugging an 8k expansion into my computer.
Anyhow, back to the plot. What I've learned so far is that that the 'less than a tenner' Raspberry Pi Zero W is 'bare bones'. I've bought a few bits and pieces that have cost much more than the computer(!) including a header for the GPI pins, a breadboard & components kit, pre-loaded micro SD (effectively the HD and OS), mini HDMI to proper-size HDMI adaptor.