You need to install the file (which should be called plug.vim) in the
directory ~/.vim/autoload. (The "~" here means your home directory.) You can
ensure that the directory exists by running this command at the command
line:
mkdir -p ~/.vim/autoload
Then move or copy the plug.vim file into the "autoload" directory.
Alternatively, the vim-plug README [1] provides a single command you can run
that will create the directory if necessary, download the file, and save it
into the right place:
curl -fLo ~/.vim/autoload/plug.vim --create-dirs \
https://raw.githubusercontent.com/junegunn/vim-plug/master/plug.vim
Hope this helps,
Benjamin
[1]
https://github.com/junegunn/vim-plug#installation