A real roleplaying scenario! This is how it works:
You actually say what you're character is doing e.g. "Bellatrix walked across the room and knelt beside the Dark Lord, 'I will always be faithful to you'"

Don't control other peoples' characters e.g. "Voldemort replied, 'Thank you Bella'


Aaaand the scene is as follows:

The final battle, in the clearing waiting for Harry to appear. The Deatheaters are chatting amongst themselves. Voldemort is seated above the rest on a fallen tree.