Your drive can be accessed from the /mnt/ directory in WSL.
With that said if you can simply navigate to /mnt/c/Users/{windows.user}/Downloads/ - replacing {windows.user} with your exact windows username, you'll be able to see all downloads that have been downloaded in windows.
Think of the directory of /mnt/c as a shortcut to the C: drive directory.
So in order to copy a file from windows to say the home directory of the current WSL user, you can use either the cp (copy) or the mv (move) commands like so:
# say the windows user name is Saleem for this example
$ cp /mnt/c/Users/Saleem/Downloads/aws.pem ~/aws.pem
# to move a file (cut/paste)
$ mv /mnt/c/Users/Saleem/Downloads/aws.pem ~/aws.pem
The syntax for cp is cp [options] SOURCE DEST,
and for mv is mv [options] SOURCE DEST
the [options] argument is optional.
as long as you are dealing with files its the same syntax, but for directories, you'd pass -R or -r (recurse through directories) option to cp, while mv just works for both files and directories without any extra options.
To learn more about usage of linux commands use man {command}, this will display the man pages of the command in question, which is a documentation for usage/features for the command.
