C++ may eventually add graphics into the standard (they were considering it), but for right now, the C++ standard does not include graphics.
You can take advantage of other standards in order to write a pixel to the screen, though. If you're on Linux, there is already an answer up.
If you're using VGA, you can actually write directly to the VGA buffer (WARNING: WAY OUTDATED Like "meant for DOS" outdated). You would probably use C++'s inline assembly to set the render mode instead of whatever that page uses, then use a regular unsigned char*
instead of a "far" pointer to access it. Although you probably aren't using VGA and probably don't want to use assembly (especially inline assembly).
So what do you do outside of that? Nothing, really. You need to use an external library specifically to render, so probably OpenGL or DirectX or some library making use of either.