At first you have to select a GUI framework:
List of platform-independent GUI libraries - Wikipedia[
^].
All of those provide documention with tutorials and example code. So you might try out some of them before doing the final decision.
Because you are using CodeBlocks, you should have at least a look at wxWidgets:
WxWindowsQuickRef - CodeBlocks[
^].
Qt has it's own QtCreator IDE available for multiple platforms. While you can also build Qt applications with CodeBlocks, the QtCreator includes design tools which makes designing the GUI and connecting to code (e.g. events like button clicks) much simpler.