Drawing a circle with an angle using TikZ

One (somehow verbose) option:

The code:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{angles,quotes}

\def\myrad{3cm}% radius of the circle
\def\myang{60}% angle for the arc

\begin{document}

\begin{tikzpicture}
% the origin
\coordinate (O) at (0,0);
% the circle and the dot at the origin
\draw (O) node[circle,inner sep=1.5pt,fill] {} circle [radius=\myrad];
% the ``\theta'' arc
\draw 
  (\myrad,0) coordinate (xcoord) -- 
  node[midway,below] {$r$} (O) -- 
  (\myang:\myrad) coordinate (slcoord)
  pic [draw,->,angle radius=1cm,"$\theta$"] {angle = xcoord--O--slcoord};
% the outer ``s'' arc
\draw[|-|]
  (\myrad+10pt,0)
  arc[start angle=0,end angle=\myang,radius=\myrad+10pt]
  node[midway,fill=white] {$s$};
\end{tikzpicture}

\end{document}

A PSTricks solution:

\documentclass{article}

\usepackage{pstricks}
\usepackage{xfp}

% parameters
\def\angle{50}
\def\radius{3}

\begin{document}

\begin{pspicture}%
 (-\radius,-\radius)%
 (\fpeval{\radius+0.4},\fpeval{max((\radius+0.4)*sin(\angle*pi/180),\radius)})
  \pscircle(0,0){\radius}
  \psline(\radius;\angle)(0,0)(\radius;0)
  \psarc{|-|}{\fpeval{\radius+0.3}}{0}{\angle}
  \rput(\fpeval{\radius/2},-0.2){$r$}
  \rput*(\fpeval{(\radius+0.3)*cos(\angle/2*pi/180)},
         \fpeval{(\radius+0.3)*sin(\angle/2*pi/180)}){$s$}
  \psarc{->}{\fpeval{\radius/6}}{0}{\angle}
  \rput(\fpeval{(\radius/6+0.25)*cos(\angle/2*pi/180)},
        \fpeval{(\radius/6+0.25)*sin(\angle/2*pi/180)}){$\theta$}
\end{pspicture}

\end{document}

All you have to do is choose the values of the parameters and the drawing will be adjusted accordingly.

Just a finger warm-up exercise with PSTricks.

\documentclass[pstricks,borde=12pt,12pt]{standalone}
\usepackage{pst-eucl}

\begin{document}
\begin{pspicture}[dimen=m](-3,-3)(3,3)
    \pstGeonode[PointName=none,PointSymbol={default,none}]{O}(2;0){A}(2;60){B}
    \pscircle{2}
    \psline(B)(O)(A)
    \pstMarkAngle[MarkAngleRadius=.9,LabelSep=.5,arrows=->]{A}{O}{B}{$\theta$}
    \pcline[linestyle=none](O)(A)\nbput{$r$}
    \psarc{|*-|*}(O){2.3}{(A)}{(B)}
    \rput*{-30}(2.3;30){$s$}
\end{pspicture}
\end{document}