#include<stdio.h>: Let's Break This Expression:-
stdio.h simply is the 'abbreviation' for "Standard-Input-Output-Header" and it's a file that contains all the function prototypes and definitions(which is the specific task that the function performs when it is called).
#include is a directive that tells the preprocessor (translator) to literally include all the content of the files in the source code(the program you write in an HIGH LEVEL PROGRAMMING LANGUAGE).
Hope It's Clear.