Hardware is the stuff you can touch. Any computing device will have a brain, a way for you to see what is happening and at least one way for you to tell the brain what to do.
Desktop computers have the components in different pieces. Tower, monitor (screen), keyboard, mouse. Modern monitors are often touch screen, which lets you use your finger just as you would on a tablet or phone. Desktops often have more power than laptops and are easier to upgrade. The larger monitors and ability to have more than one monitor make them a good choice for fixed location use.
Laptops have the screen, brain, and keyboard built together for portability. Most will have a touch pad – a sensitive area of the case that lets you move the pointer on screen around by moving your finger in the touch sensitive box. Touch screens are becoming more popular on laptops as well. Laptops can be very small, light and portable, but at the expense of power and ease of use for touch typists. Larger laptops allow for standard keyboards and larger screens, but at the expense of extra weight that can make them harder to carry along.
Tablets generally don’t have a keyboard as an integral part, although they do have a “soft keyboard” that will appear on the touch screen when needed. The lines are blurring between laptops and tablets with laptops getting smaller and tablets getting bigger and both running the same software. (A topic for another post.) Tablets are lighter and easier to carry than most laptops, but also less flexible for expanding. They are good for specially developed games, email, social sites, videos and reading digital books. There is even software that lets them make video calls.
Phones almost never have a physical keyboard anymore. Like tablets, they have soft keyboards on the screen. The line between tablets and phones has blurred with phones getting bigger and tablets being able to answer phone calls. A phone’s primary purpose is to make and receive calls. But with the larger screens, they can do most of the same things a tablet can.