Hard drive and SSD
A hard drive stores all of the data which isnt in use at the moment. It contains moving parts which means that when it gets shaken it breaks, which is a major disadvantage and also it is rather large.
The SSD is a smaller version of a hard drive and it doesn't break when shaken. It also is alot faster but are more expensive.
Optical Drive, Moniter, CPU and RAM
RAM stands for random accessing memory. It stores all the data which you aren’t using at the moment.