1+1   (* To evaluate an expression, you press Shift+Enter NOT just Enter *)

s1 = ParametricPlot[ 
{r Cos[t],r Sin[t]},  (* Ordered pair written with curly brackets: {a,b} NOT (a,b). 
Built-in functions have capital letters: Exp  NOT  exp
  Function evaluation uses square brackets: Cos[t], NOT Cos(t)  *)
{r,0,1},{t,0,2 Pi},Mesh->{5,11}, (* Mesh controls # grid lines*)
Axes->True, Frame->False,PlotStyle->{Red} (* Check out Plot options in Help *)
]   (* This bracket closes ParametricPlot *)

s2 = ParametricPlot[ 
{r Cos[t],r Sin[t]}, 
{r,2,3},{t,0,2 Pi},Mesh->{5,11}, 
Axes->True, Frame->False,PlotStyle->{Green}
]

Show[s2,s1]  (* Display several graphics objects in same plane. *)