first, please verify that you can compile and run your hello_world.cpp from the commandline:
g++ -Wall hello_world.cpp && ./a.out
Then start Code::Blocks and check, if your compiler path and executables are
set correctly (see: settings|compiler|toolchain executables. Probably, your
path for the selected GNU GCC Compiler should be /usr and the C++ Compiler g++.
In Order to see the executed commands when you start to compile, please
go to settings|compiler|other settings and select as compiler protocol:
full commandline. Once, you have closed the settings, open view|Logs (F2).
When you start compiling your hello world project from inside Code::Blocks,
the appropriate commands should show up the logs.
If compiling and linking were sucessfull, the binary for target Debug is
by default in the project's subdirectory bin/Debug. This you can start
from Code::Blocks or from the commandline.
I hope, this helps.