Tjyylli

MWE:

documentclass[12pt]{article}

usepackage{pgf}

usepackage{tikz}

usepackage{pgfplots}

begin{document}

    begin{tikzpicture}

    draw [line width=1pt] (0,5)-- (0,0);

    draw [line width=1pt] (5,0)-- (0,5);

    draw [line width=1pt] (0,0)-- (5,0);

    draw [fill=black] (0,5) circle (1.5pt);

    draw[color=black] (0.0,5.5) node {$A$};

    draw [fill=black] (0,0) circle (1.5pt);

    draw[color=black] (0.0,-0.5) node {$B$};

    draw [fill=black] (5,0) circle (1.5pt);

    draw[color=black] (5.0,-0.5) node {$C$};

    end{tikzpicture}

end{document}

Question:

How can I draw direction arrow on each lines of triangle? (all possible style of arrows)

Maybe I misread the question, but if you want to vary the type of the arrow you may want to use

documentclass[12pt]{article} 

usepackage{tikz} 

usetikzlibrary{decorations.markings}

begin{document}

% based on https://tex.stackexchange.com/a/39282/121799

tikzset{->-/.style n args={2}{decoration={

  markings,

  mark=at position #1 with {arrow{#2}}},postaction={decorate}}}

begin{tikzpicture}[bullet/.style={circle,inner sep=1.5pt,fill}] 

 path  (0,5) node[bullet,label=above:$A$](A){}

  (0,0) node[bullet,label=below:$B$](B) {}

  (5,0) node[bullet,label=below:$C$](C) {};

  foreach X/Arrow [remember=X as LastX (initially C)]in

  {A/latex,B/stealth,C/>}

  {draw[line width=1pt,->-={0.5}{Arrow}] (LastX) -- (X);}

end{tikzpicture} 

end{document}

As for your comment: this draws three triangles. Is that what you are looking for?

documentclass[12pt]{article} 

usepackage{tikz} 

usetikzlibrary{decorations.markings}

begin{document}

% based on https://tex.stackexchange.com/a/39282/121799

tikzset{->-/.style n args={2}{decoration={

  markings,

  mark=at position #1 with {arrow[line width=1pt]{#2}}},postaction={decorate}}}

begin{tikzpicture}[bullet/.style={circle,inner sep=1.5pt,fill}] 

 begin{scope}

  path  (0,5) node[bullet,label=above:$A$](A){}

   (0,0) node[bullet,label=below:$B$](B) {}

   (5,0) node[bullet,label=below:$C$](C) {};

   foreach X [remember=X as LastX (initially C)] in  {A,B,C}

   {draw[line width=1pt,->-={0.5}{latex}] (LastX) -- (X);}

  end{scope} 

 begin{scope}[xshift=6cm]

  path  (0,5) node[bullet,label=above:$A$](A'){}

   (0,0) node[bullet,label=below:$B$](B') {}

   (5,0) node[bullet,label=below:$C$](C') {};

   foreach X [remember=X as LastX (initially C')]in  {A',B',C'}

   {draw[line width=1pt,->-={0.5}{stealth}] (LastX) -- (X);}

  end{scope} 

  begin{scope}[yshift=-6.6cm]

  path  (0,5) node[bullet,label=above:$A$](A''){}

   (0,0) node[bullet,label=below:$B$](B'') {}

   (5,0) node[bullet,label=below:$C$](C'') {};

   foreach X [remember=X as LastX (initially C'')]in  {A'',B'',C''}

   {draw[line width=1pt,->-={0.5}{>}] (LastX) -- (X);}

  end{scope} 

end{tikzpicture} 

end{document}

Using TikZ: How to draw an arrow in the middle of the line?

%documentclass[border=2mm]{standalone}

documentclass{article}

usepackage{tikz}

usetikzlibrary{decorations.markings}

begin{document}

begin{tikzpicture}



    draw [fill=black] (0,5) circle (1.5pt);

    draw[color=black] (0.0,5.5) node {$A$};

    draw [fill=black] (0,0) circle (1.5pt);

    draw[color=black] (0.0,-0.5) node {$B$};

    draw [fill=black] (5,0) circle (1.5pt);

    draw[color=black] (5.0,-0.5) node {$C$};



begin{scope}[very thick,decoration={

    markings,

    mark=at position 0.5 with {arrow{>}}}

    ] 

    draw [line width=1pt,postaction={decorate}] (0,5)-- (0,0);

    draw [line width=1pt,postaction={decorate}] (5,0)-- (0,5);

    draw [line width=1pt,postaction={decorate}] (0,0)-- (5,0);

end{scope}

end{tikzpicture}

end{document}