ContourPlot3D[x^2+y^2==z^2,{x,-5,5},{y,-5,5},{z,-5,5}]

ContourPlot3D[x^2+y^2==z^2,{x,-5,5},{y,-5,5},{z,-5,5}, Mesh->None,ContourStyle->Cyan]

ContourPlot3D[x^2+y^2==z^2,{x,-2,2},{y,-2,2},{z,-2,2},ColorFunction->Function[{x,y,z,f},Hue[Sin[x]Sin[y]]],Mesh->None]

ContourPlot3D[{x^2+y^2==z^2,x+2*y+z==10},{x,-5,5},{y,-5,5},{z,-5,5},Mesh->None]

ContourPlot3D[{x-y-z==1,x^2+y^2==z^2},{x,-2,2},{y,-2,2},{z,-2,2},Mesh->None,ContourStyle->{Green,Brown}]

aux=100;
aux1=20;
ContourPlot3D[{x^2+y^2==z^2,2*x+2*y+2*z==2},
{x,-aux1,aux1},{y,-aux1,aux1},{z,-aux1,aux1},
Mesh->None,
ContourStyle->{Directive[Orange,Opacity[0.5]],Directive[Blue,Opacity[0.5]]}]

aux=100;
aux1=7;
Animate[
ContourPlot3D[{x^2+y^2==z^2,a*x+b*y+c*z==d},
{x,-aux1,aux1},{y,-aux1,aux1},{z,-aux1,aux1},
Mesh->None,
ContourStyle->{Directive[Orange,Opacity[0.7]],Directive[Blue,Opacity[0.5]]}
],{a,-aux,aux},{b,-aux,aux},{c,-aux,aux},{d,-aux,aux},AnimationRunning->False]

aux=100;
aux1=10
;
Animate[
ContourPlot3D[{x^2+y^2==z^2,a*x+b*y+Sqrt[a^2+b^2]*z==d},
{x,-aux1,aux1},{y,-aux1,aux1},{z,-aux1,aux1},
Mesh->None,
ContourStyle->{Directive[Orange,Opacity[0.7]],Directive[Blue,Opacity[0.5]]}
],{a,-aux,aux},{b,-aux,aux},{d,-aux,aux},AnimationRunning->False]