A tiny computer
A Raspberry Pi is a very small computer, roughly the size of a credit card (though considerably thicker), that comes with a CPU, RAM, some USB ports, a network port, an SD card port, and little else.
It’s not meant to be a replacement for a real computer, though people have used them that way, but for $35 you get a tiny brain that can power your homebuilt devices.
To put things into perspective, at best you can expect this thing to have the power of a smartphone, and not even a top of the line smartphone.
$35 buys you the computing part of the computer, not the input or output parts, so you will have to also buy a monitor of some kind (you can use a TV), a mouse, a keyboard, an SD card (onto which you will have to install an operating system, since it doesn’t come with one), any other peripherals you may want to add (like a WiFi or bluetooth dongle for example), and even a power source (a phone charger should do).
In the end, you will probably spend close to what you would for a low end computer or Chromebook, so if you’re looking for a computer you probably have better options.
The little engine that could
Having said that, if you’re looking for the brains of your homebuilt automatic cat feeder, or homemade weather station, or fighting robot, or even old Gameboy emulator, or a complicated way to turn a regular hard drive into a NAS hard drive then the Pi might be for you.
It’s basically a hobbyist’s device, more than a device for the general public, but if you like to tinker with your electronics, you may enjoy playing around with one, just be aware of it’s limitations.
Raspberry Pi computers are excellent in schools, especially science labs, as students get to understand the inner workings of the computer. It’s like one of those skinless human body mannequins that lurk in the corners of science labs and expose muscles, bones, and organs to the unwary student.
In short, a great device–in its place. Not exactly a consumer tech product, though.