뭐 하고 있나요? 뭐 하고 있어요? What are you doing? ("있어요?" is more common) 밥은 먹었나요? 밥은 먹었어요? Did you eat yet? ("먹었어요?" is more common) 식사 했어요? 식사 하셨어요? is also widely used to mean the same thing.

ahh..thank you guys so much! it helped me~

은혜's answer is great. just plus, 밥은 먹었나요? can also mean 'Did you have a meal?'

I'm not a native speaker, I'm just a learner of the lang so the first sentence means "What are u doing?" the second "Have u eaten (your food)?". Hope that can help.