Formatting Local Disk (D:)

Hey guys, thanks for the help in advance. I'm not super knowledgeable about computers but I'm trying to get better so I don't have to run to my brother every time I have a question. Thanks! Sorry if I seem like I have no idea what I'm talking about.

K so, I open up 'My computer' and under 'hard disk drives' there is 'C' and 'D'. C is full, so I want to transfer files to 'D' to free up some space on 'C'. Want to transfer all my downloads to 'D', just movies and music. Before I take any action with 'D' it says it must be formatted. When I try to do so, a big scary pop-up says 'WARNING: Formatting will erase ALL data on this disc' and asks my if I'm okay with that. Is that fine to proceed? Am I doing anything super duper wrong here?

By the way, its a brand new computer. Don't know if that matters at all.

Thanks:)

-Carley