The keyboard, sound card, hard drive, mouse are all peripheral devices. In fact anything that is is plugged into an extension slot. Some devices may any be used for specialist applications, such as a graphics tablet, or webcam, others may be essential for accessibility reasons. A Braille reader for example.
Along with these devices, a piece of software called a driver is required, to interface the device to the computer. Without it the device won't work. Unfortunately there are still suppliers who do not supply drivers that work with Linux, consequently some care must be taken when buying new devices. and its always a good idea to check the internet to ensure a driver exists.
This can be particularly true for products new to the market.