Why my leader key is not working for y,d,p?

I have some mappings define for "+y, "+p, "+d .. But none of the mappings are working. When I press leader key (,) and then press y or d or p or P, I get beep sound. Can anyone help me why is it not working? Here is my ~/.vimrc content:

 cat ~/.vimrc

call plug#begin()

" List your plugins here

Plug 'elixir-editors/vim-elixir'

Plug 'itchyny/lightline.vim'

Plug 'jaredgorski/spacecamp'

call plug