Vim and indentation

Tab: default behavior of vim is: add &tabstop spaces unless expandtab is not set. You can always insert real tabs by <c-v><tab>. However tabstob should be treated as display setting. Use sw setting and c-t, c-d instead.

  c-t: increase indentation
  c-d: decrease indentation
  c-f: auto indent current line (requires indentation setup)
  :setlocal sw=4: use 4 spacse for indentation
  :setlocal expandtab: expand tab to spaces (default)
  :setlocal tabstop: a tab is viewed as how many spaces in a file?

  :set list  : displays spaces and tabs

Where to set those options?: See configuring-vim

how to make vim reindent lines ?

The :h = is the command which is commonly used for using the Vim's indentation features. Some use cases:

gg=G: reindent whole file
>3j . .  increase indentation of 3 lines and repeat two times
V/ABC<cr>=  :select everything till ABC then reindent this block