\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{shapes.misc, positioning, backgrounds, fit}

\begin{document}

\begin{tikzpicture}[node distance=1 and 1]
  \draw[help lines, very thin] (-1,-3) grid (5, 1);
  % Drawing boxes left aligned
  \node at (0,0) [rectangle,white,fill=red] (D) {D};
  \node [rectangle,white,fill=blue,below=of D.west,anchor=west] (E) {EFGH};
  \node [rectangle,white,fill=blue,anchor=south,on grid, below=of E.west,anchor=west] (F) {RST};

  % Drawing boxes center aligned
  \node at (2,0) [rectangle,white,fill=red] (A) {A};
  \node [rectangle,white,fill=blue,on grid, below=of A] (B) {BCD};
  \node [rectangle,white,fill=blue,on grid, below=of B] (C) {PQRS};

  % Drawing boxes right aligned
  \node at (4,0) [rectangle,white,fill=red] (G) {G};
  \node [rectangle,white,fill=blue,on grid, below=of G.east,anchor=east] (H) {EFGH};
  \node [rectangle,white,fill=blue,anchor=south,below=of H.east,anchor=east] (F) {RST};
\end{tikzpicture}

\end{document}