There are 4 main concepts which react is made of and are the reasons of its popularity.
1- React manipulates the DOM, so no need to manipulate it directly!!
2- React builds the website from individual, separated components.
3- Data can flow in one direction.
As it could be seen in below image, data could flow from parent component to its Childs and grand-Childs and the update in states could send back to parent nodes and again new data will flow from up to bottom. In other words, sibling nodes or grand-siblings node doesn’t have access to their data and this architecture, somehow, increases the speed of data flow and updates in states and eventually the speed of page load.
4- React is the UI, the rest is up to you.