Resources in Crusade are per colony not global like they were pre-crusade. Your resources on the top bar is you stockpile of resources. You use these for any number of things, starbase upgrades, promotions, improvement upgrade, weapons and probably a couple I have missed. Once used it is gone and you have to regenerate your stockpile. Information on said resouce can be found on the tooltip when your in the planet screen. (Hover over the resource)
Pre Crusade they all give a global 5% bonus, and yes it stacks. So do not trade them away if you can help it 
