As a command: Nobody move! Nobody talk! Everyone sit! This is very important and I need your full attention. As a description: Nobody moves. Nobody talks. Everyone sits. It's very boring in my class.

If you are ordering a group of people not to move, you say "nobody move." You could also give the same order to one person, "Don't move!" By the way, another way to give the order is "Freeze!" If you are describing a situation, in the present tense, you say "nobody moves." You might do this when telling a story in the historical present. "Captain Queeg walks into the wardroom. He's furious. He shouts 'Who ate the strawberries?' Nobody speaks. Nobody moves." In the past tense, you would say "nobody moved." "Captain Queeq walked into the wardroom. He was furious. He shouted 'Who ate the strawberries?' Nobody spoke. Nobody moved."

Hi, Tiger! If you use it in Simple Past Tense, you have to say "Everybody moves". However, if you want to give an order, (imperative form) you have to use "Everybody move!". First of all, you should pay attention to what you really mean in order to find the best way of expressing what you want. The direct translation does not work sometimes. Regards!

Nobody move - it is imperative/instructional rather than descriptive/present. Hope that helps!