"drive" means "partition" in that context, unless you have more than one physical hard drive in your computer.
assuming you have only one hard drive, you will have to repartition some space (i.e., a dedicated partition) for your linux install. repartitioning and the reformatting you will have to do after will delete any data that's on that drive (edit: meaning partition
) that you reformat. thanks to windows, it seems your C: drive is taking up the bulk of the disk, so the process is not going to be easy without something like partition magic.