Graph with line and parenthesis

Question

I am quite new to graphing in latex and need the following example:

I have no idea what package to use to generate the curly bracket over the red line and the label that goes with it.

An example of the code would be appreciated

PS: I do not provide a preamble because I am not sure of the packages needed.

Answer 1

\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{decorations.pathreplacing,calligraphy}
\begin{document}
\begin{tikzpicture}
 \draw[thick,stealth-stealth] (0,6.5) |- (6.5,0);
 \draw foreach \x in {1,...,5} {(\x,0.1) -- (\x,-0.1) node[below]{$\x$}
    (0.1,\x) -- (-0.1,\x) node[left]{$\x$}};
 \draw[dashed] foreach \x in {1,3,5 }{(\x,0) |- (0,\x)};
 \draw[red,thick] (3,3) -- (5,5);
 \draw[thick,decorate,decoration={calligraphic brace,raise=0.5ex}]
    (3,3) -- node[above left=0.6ex,align=center,font=\sffamily]{Completed\\
        Strategies}(5,5);
\end{tikzpicture}
\end{document}