documentclass[tikz,border=2mm]{standalone}
usepackage{bm}

begin{document}

    begin{tikzpicture}

        node[circle,draw] at (0,0) (n1) {A};
        node[circle,draw] at (5,0) (n2) {B};

        draw[->] (n1) -- node[above]{$bm{w_1}$} (n2);

    end{tikzpicture}

end{document}