do you know how functions work? If not then I don't think it's wise jumping straight into making a game. Have you completed the lite-c workshops?

If you do understand functions then you create a different function for the different sections of the game. In your case you can have 2 functions; 1 for story mode and 1 for endurance mode. We have 2 functions as they do different things.

function EnterStoryMode()
{
// load story mode stuff
}

function EnterEnduranceMode()
{
// load endurance mode stuff
}

Then going back to your PANEL*, for each button you replace the "FunctionOn" argument with the name of the function you want to run...

button(0, 0, goclick, gonorm, goover, EnterStoryMode, NULL, NULL)