React component :
React is all about components. Because all user interfaces in the end are made up of components.
component are like function that returns Html elements .
component are independent and reusable bit of code .
they serve the same purpose as JS functions, but work in isolation and retun Html .
Component come in two types, class & Functional component
How components will communicate like parent - > child , sibling , discedent.

Re-Use-component :
For Example there is a div element that has some text inside it .
If I want to replicate it .
I will have to write the same div element again, what we can insted do is extract the div element inside a variable and write that element directly in my app's JSX.