\def\a{3}
\def\b{3}
\def\r{2cm}

\begin{tikzpicture}
	\foreach \i in {1,...,\a} 
        \node[draw, small vertex] (a-\i) at (\i*\r, \r) {};
		
	\foreach \i in {1,...,\b} 
        \node[draw, small vertex] (b-\i) at (\i*\r, 0) {};
	
    \foreach \u in {1,...,\a}
		\foreach \v in {1,...,\b}
			\draw (a-\u) -- (b-\v);
\end{tikzpicture}
