Some Example from the net

Drawing midway arrow:

\usepackage{tikz}
\usetikzlibrary{decorations.markings}

\begin{document}
\begin{tikzpicture}
% draw the two circles and decorate them with arrows
\draw[
decoration={markings, mark=at position 0.625 with {\arrow{>}}},
postaction={decorate}
]
(0,0) circle (0.5);
\draw[
decoration={markings, mark=at position 0.125 with {\arrow{>}}},
postaction={decorate}
]
(3,0) circle (0.5);

% draw the connecting line
\draw[
decoration={markings, mark=at position 0.5 with {\arrow{>}}},
postaction={decorate}
]
(0.5,0) -- (2.5,0);

% draw the two black dots
\fill (0.5,0) circle (0.1);
\fill (2.5,0) circle (0.1);
\end{tikzpicture}