Argthtjtr

I am completely new to tikz so excuse me if it seems easy.
I am going to put a label inside the closed path I have written(mostly taken from here):

begin{tikzpicture}[->,>=stealth',shorten >=1pt,auto,node distance=3cm,

                thick,main node/.style={circle,draw,font=Largebfseries}]

  node[main node] (2) {2};

  node[main node] (1) [below left  of=2] {1};

  node[main node] (3) [below right of=2] {3};

  path

    (1) edge node [below]{} (2)

        edge node[below] {} (3)     

    (2) edge node[right] {} (3)

    (3) ;

end{tikzpicture}

Thanks for any guide.

If you don't know which "center" you're talking about, I suggest you use the barycentric coordinates to do so. (See pages 136 et seq. of manual 3.1
13.2.2 Barycentric Systems)

documentclass[tikz,border=5mm]{standalone}

usetikzlibrary{arrows}





begin{document}

begin{tikzpicture}[->,>=stealth',shorten >=1pt,auto,node distance=3cm,

                thick,main node/.style={circle,draw,font=Largebfseries}]

  node[main node] (2) {2};

  node[main node] (1) [below left  of=2] {1};

  node[main node] (3) [below right of=2] {3};

  path

    (1) edge node [below]{} (2)

        edge node[below] {} (3)     

    (2) edge node[right] {} (3)

    (3) ;

  node at (barycentric cs:1=1,2=1 ,3=1) {Text};

end{tikzpicture}

end{document}

off-topic:

• use only numbers for node names is not good practice. instead 1, 2 and 3 is better to use for example n1, or n2 and n3
  


• if you not label edges than don't clutter code with empty nodes.


• for labeling of edges is handy to use quotes library


• at using barycentric coordinates be careful: between colon or comas and node names had not be an empty space


• it seems that you have a mess in code for drawing arrows

using solution for placing nodes inside triangle suggested in @AndréC answer (+1) the mwe can be as follows:

documentclass[tikz, margin=3mm]{standalone}

usetikzlibrary{arrows.meta, positioning, quotes}



begin{document}

    begin{tikzpicture}[

           node distance = 17.3mm and 10mm,

       every edge/.style = {draw, semithick, -Stealth, shorten >=1pt},

every edge quotes/.style = {inner sep=1pt,

                            font=footnotesize, text=gray,

                            sloped, auto=left},

             main/.style = {circle, draw, semithick,

                            minimum size=3ex, inner sep=2pt,

                            font=bfseries}

                        ]

node (n1) [main] {1};

node (n2) [main, above right=of n1] {2};

node (n3) [main, below right=of n2] {3};



% note: between ":" or "," and "<node name>" had not to be empty space!

node at (barycentric cs:n1=1 ,n2=1 ,n3=1) {text};



draw   (n1) edge ["2" ']    (n3)

        (n1) edge ["3"]      (n2)

        (n2) edge ["1"]      (n3);

    end{tikzpicture}

end{document}