documentclass{standalone}
usepackage{tikz}
usetikzlibrary{shapes.geometric}

begin{document}
begin{tikzpicture}
  draw[style=help lines] (0, 0) grid (5, 5);
  node (a) [rectangle, draw, fill=red!20]   at (1, 1) {Rectangle A};
  node (b) [rectangle, draw, fill=green!20] at (4, 4) {Rectangle B};
  node (c) [rectangle, draw, fill=blue!20]  at (4, 1) {Rectangle C};
end{tikzpicture}
end{document}