Install Python3 via homebrew (Optional: in case you do not have pyhton installed. run python3 --version to see if it's installed)
$ brew install python3
Install powerline via pip (python package manager)
$ pip3 install powerline-status
If you don't have .vimrc file in your home directory, create one.
$ touch ~/.vimrc
Open .vimrc
in your editor and paste this code.
" powerline
set rtp+=/usr/local/lib/python3.6/site-packages/powerline/bindings/vim
set laststatus=2