I am entering to my schedule work values for each task. For example I said surveying will take 10 hours, foundation formwork will take 100 hours etc... all by labor so it is fine if ms project adds them together. but how about excavating the site. it is work by excavator not human. but the work is still added to work of other tasks in the summary task. the difference will be in the hourly rate of a human labor vs an excavator, which will be much more expensive correct?

I assume it is work for both the excavator (machine) and the driver of the excavator. If you need to track a potential over-allocation of the excavator (machine) it will need to be a work resource. If you are confident that excavator is available and you only want to track labor (human) work, add the cost for the excavator as either a cost resource or a fixed cost to the task.