σ=10;
b=8.0/3;
r=28;
tend=100;
s=NDSolve[{x'[t]==σ*(y[t]-x[t]),y'[t]==x[t]*(r-z[t])-y[t],z'[t]==x[t]*y[t]-b*z[t],x[0]==10,y[0]==10,z[0]==10},{x,y,z},{t,0,tend}];
Plot[x[t]/.s,{t,0,tend}]

σ=10;
b=8.0/3;
r=28;
tend=100;
s=NDSolve[{x'[t]==σ*(y[t]-x[t]),y'[t]==x[t]*(r-z[t])-y[t],z'[t]==x[t]*y[t]-b*z[t],x[0]==10,y[0]==10,z[0]==10},{x,y,z},{t,0,tend}];
ParametricPlot3D[{x[t],y[t],z[t]}/.s,{t,0,tend}]

s2=NDSolve[{x'[t]==σ*(y[t]-x[t]),y'[t]==x[t]*(r-z[t])-y[t],z'[t]==x[t]*y[t]-b*z[t],x[0]==0,y[0]==1,z[0]==2},{x,y,z},{t,0,tend}];
ParametricPlot3D[{x[t],y[t],z[t]}/.s2,{t,0,tend}]

ParametricPlot[{{x[t],z[t]}/.s,{x[t],z[t]}/.s2},{t,0,tend}]