Why use public, protected, and private objects?

Question

Classes and objects are super confusing to me. Im starting with clarifying this

Answer 1

i'm korean so my english so bad. for example you have a object that name is computer. cable,RAM,HDD are private in computer class. that is, other people is just want what power switch,keyboard,monitor. that's public object. you don't show other people to object and variables. you should make the private. but you show their to object and variables? so you use the public keyword.