Mryntu

MWE:

documentclass[12pt]article
usepackagepgf
usepackagetikz
usepackagepgfplots
begindocument
 begintikzpicture
 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 $C$;
 endtikzpicture
enddocument

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 
usepackagetikz 
usetikzlibrarydecorations.markings
begindocument
% based on https://tex.stackexchange.com/a/39282/121799
tikzset->-/.style n args=2decoration=
 markings,
 mark=at position #1 with arrow#2,postaction=decorate
begintikzpicture[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,->-=0.5Arrow] (LastX) -- (X);
endtikzpicture 
enddocument

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

documentclass[12pt]article 
usepackagetikz 
usetikzlibrarydecorations.markings
begindocument
% based on https://tex.stackexchange.com/a/39282/121799
tikzset->-/.style n args=2decoration=
 markings,
 mark=at position #1 with arrow[line width=1pt]#2,postaction=decorate
begintikzpicture[bullet/.style=circle,inner sep=1.5pt,fill] 
 beginscope
 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,->-=0.5latex] (LastX) -- (X);
 endscope 
 beginscope[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,->-=0.5stealth] (LastX) -- (X);
 endscope 
 beginscope[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);
 endscope 
endtikzpicture 
enddocument

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

%documentclass[border=2mm]standalone
documentclassarticle
usepackagetikz
usetikzlibrarydecorations.markings
begindocument
begintikzpicture

 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 $C$;

beginscope[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);
endscope
endtikzpicture
enddocument