For redefine tabs to space (whatever many spaces, the development default is four) is very simple.

Open the ~/.vimrc:

vim ~/.vimrc

So, paste the configuration into the file:

set tabstop=4       " The width of a TAB is set to 4.
                    " Still it is a \t. It is just that
                    " Vim will interpret it to be having
                    " a width of 4.
set shiftwidth=4    " Indents will have a width of 4
set softtabstop=4   " Sets the number of columns for a TAB
set expandtab       " Expand TABs to spaces

Save and restart (:wq!) vim.