What does this mean in C++ programming?

Question

cout << "Enter a number: ";
cin >> a;

Answer 1

cout means console output so when you use
cout<<"Enter a number"; it displays the message "Enter a number on screen.

cin means console input and when you use
cin>>a;
it reads the keyboard(what key you press) and stores it into the variable a;

Answer 2

cout << "Enter a number: "; means that standard output, print this string "Enter a number:" (without ")
cin>>a means that enter a variable like integer or float or a character, it depends on what you defined it.

Answer 3

ask user to enter a number in console ie black monitor screeen
when user inputs or enter no. thru keyboard store that value to memory a representing

Answer 4

It prints out on the computer:

Enter a number.

Then it reads the nunmber that the user types and put the number in the variable a.

Answer 5

this means you are printing on the console : Enter a number
and taking input from the console.

note that, from console i mean your monitor,
although to be more precise, it is the standard input/output streams.