The insertion operator symbol is <<.
It is used for program output. (The same symbol is also used for a different operator! The types of the operands determine wich operator is meant.)
There are two quite different facilities for program input and output (I/O) in C++. One library, the standard io library is older and was developed for C. A newer library for io was added when C was extended to C++. One sees both libraries in use. In particular, the much of older C style i/o library functionality and similar form has been recently added to Java. Some people find it more convenient (once they have learned how to use it).
The insertion operator is used in the newer C++ I/O library.
The insertion operator is a binary operator.
Its left operand should be of type ostream - output stream.
The right operand can be any of the built in data types such as char, int, float, double, string and can be extended to other data types.