Hardware is the physical part of any technology. For Computers, there are several physical elements you would need. There are two requirements for any device. First is a power source often called a power supply.  Second is where it is housed. In many cases, they are housed in a mini-tower or just a case that has many connections. 

All parts connect to a Motherboard or Central point. Motherboards connect various components together inside such as:

Processor

Hard Drive

RAM aka Memory

Video Card

Outside the Motherboard, there are many external devices that can be connected to the Computer via either USB, network, or wireless technologies. Examples include:

Printers

Keyboards

Mouses

Network

Flash Drive or External Hard Drive

Monitors