Hard drive and SSD
A hard drive is a device in a computer which holds all the computers' memory. Everything from applications, to picture to files. Without the hard drive the computer is useless. It works with an arm and a disk, everthing you download or save is written on to the disk by the arm.
An SSD is like a hard drive but it's smaller and thinner and doesn't work with an arm and disk. It simply stores all your memory on to the device. SSDs are used for thinner devices like Ipads and laptops. However it is more expensive yet it holds less than a hard drive. Say a hard drive held 6GB the SSD could probably only hold about 4GB.
The motherboard is the centre of the computer, everything is conected to it. Monitor cables, RAMs, hard drives, everything. It has a fan to cool the computer down when it gets too hot, when you work on a computer for long enough you can hear the fan going round.