Parametric equation plot

Clear[x1, x2, t];


eqn = {x1 & # 39;

ics = {x1[0] == 1, x2[0] == 1};

sol = NDSolve[Flatten[{eqn, ics}], {x1, x2}, {t, 0, 10}];
ParametricPlot[{x1[{x1[{x1[{x1
AxesLabel -> {x1

How can I plot x1 against x2? How can I solve and trace these equations?