Believe you are talking about one of the early tutorial levels, if I remember right just a matter of connecting the civilian housing to the command center with roads, maybe also getting a farm setup and connected also.
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If you look at your power bar on the top of the screen always want to make sure its not red, should be a kinda off white color indicating you have plenty of extra power. Turrets and capacitors don't charge quickly otherwise.
Also having some capacitors will help.