I would recommend not worrying too much. Maybe play some custome battles to get a feel for things or play a campaign on lower diffuculty settings. The best way to learn is just have a go! You will make mistakes and get beaten at times but you'll learn from your mistakes and improve! That's the luxury of the computer game, if your empire is in ruins just start a new game
Once you've played a few battles you might have some more specific question you can ask here, which should give you better help than a very broad "what the hell do I do?" kind of question
Good luck

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