Install Brew if you do not have it.

usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

Install Vim with Brew

brew install vim

Create the plugin directory under ~/.vim/

mkdir ~/.vim/plugin

Copy plugin file into that folder

cp location/of/plugin/foobar.vim ~/.vim/plugin/foobar.vim

Now you can use the plugin in Vim.