Plot3D[x^2+y^2,{x, -10, 10}, {y, -10, 10}]

Plot3D[x^2+y^2,{x, -10, 10}, {y, -10, 10}]

Manipulate[ParametricPlot3D[{ {s, t, (s)^2+(t)^2},{a, s, t}}, {s, -10, 10}, {t, -10, 10}, PlotRange->{-10, 10}], {a, -5, 5}]

Plot3D[(x^2)+(y^2),{x,-10,10},{y,-10,10},Mesh->Automatic,MeshFunctions->{#3&}]

Manipulate[ParametricPlot3D[{ {s, t, (s)^2+(t)^2},{s, t, a}}, {s, -10, 10}, {t, -10, 10}, Mesh->Automatic,MeshFunctions->{#3&}, PlotRange->{-10, 10}], {a, 0, 10}]

Plot3D[x^2-y^2,{x, -10, 10}, {y, -10, 10}]

Manipulate[ParametricPlot3D[{ {s, t, (s)^2-(t)^2},{a, s, t}}, {s, -10, 10}, {t, -10, 10}, PlotRange->{-10, 10}], {a, -3, 3}]

Manipulate[ParametricPlot3D[{ {s, t, (s)^2-(t)^2},{s, a, t}}, {s, -10, 10}, {t, -10, 10}, PlotRange->{-10, 10}], {a, -3, 3}]

Plot3D[(x^2)-(y^2),{x,-10,10},{y,-10,10},Mesh->Automatic,MeshFunctions->{#3&}]

Manipulate[ParametricPlot3D[{ {s, t, (s)^2-(t)^2},{s, t, a}}, {s, -10, 10}, {t, -10, 10}, PlotRange->{-10, 10}], {a, -10, 10}]