main() is an entry point ( main function) which is in most programming languages, When compiler begins compile the program, It looks for an entry point, and main() acts as an entry point in C program, or we can say main is a thread/ process/ function that invokes automatically by the compiler when program is being executed.
Every function returns a value to the calling function, at that time main will be a called function for compiler/OS and it will return some value to the compiler before exit, here void and int defines that main will return a void ( nothing) and int will return an integer values to the compiler.
