Clear[f,x,y];f[x_,y_]=y-x;

Plot3D[f[x,y],{x,-3,3},{y,-3,3},PlotPoints->24,AspectRatio->Automatic,AxesLabel->{x,y,z},ViewPoint->{20,8,1},PlotLabel->f[x,y]]
ContourPlot[f[x,y],{x,-5,5},{y,-5,5},ContourShading->False,PlotLabel->f[x,y]]

Clear[f,x,y];f[x_,y_]=(((y-x))^3);

Plot3D[f[x,y],{x,-3,3},{y,-3,3},PlotPoints->24,AspectRatio->Automatic,AxesLabel->{x,y,z},ViewPoint->{20,8,1},PlotLabel->f[x,y]]
ContourPlot[f[x,y],{x,-5,5},{y,-5,5},Contours->25,ContourShading->False,PlotLabel->f[x,y]]

Clear[f,x,y];
f[x_,y_]=3 ((x^2)+(y^2));
Plot3D[f[x,y],{x,-3,3},{y,-3,3},PlotPoints->24,AspectRatio->1,AxesLabel->{x,y,z},ViewPoint->{20,8,1},PlotLabel->f[x,y]]
ContourPlot[f[x,y],{x,-5,5},{y,-5,5},ContourShading->False,PlotLabel->f[x,y]]

Clear[f,x,y];
f[x_,y_]=3 (Sqrt[(x^2)+(y^2)]);
Plot3D[f[x,y],{x,-3,3},{y,-3,3},PlotPoints->24,AspectRatio->1,AxesLabel->{x,y,z},ViewPoint->{20,8,1},PlotLabel->f[x,y]]
ContourPlot[f[x,y],{x,-5,5},{y,-5,5},ContourShading->False,PlotLabel->f[x,y]]

Clear[f,x,y];
f[x_,y_]=1+3 ((((x^2)+(y^2)))^(1/4));
Plot3D[f[x,y],{x,-3,3},{y,-3,3},PlotPoints->24,AspectRatio->1,AxesLabel->{x,y,z},ViewPoint->{20,8,1},PlotLabel->f[x,y]]
ContourPlot[f[x,y],{x,-5,5},{y,-5,5},Contours->15,ContourShading->False,PlotLabel->f[x,y]]

Clear[f,x,y];f[x_,y_]=y-Sin[x];
Plot3D[f[x,y],{x,0,2 π},{y,0,7},PlotPoints->24,AspectRatio->Automatic,AxesLabel->{x,y,z},ViewPoint->{8,-20,1},PlotLabel->f[x,y]]
ContourPlot[f[x,y],{x,0,2 π},{y,0,7},ContourShading->False,PlotLabel->f[x,y]]

Clear[f,x,y];
f[x_,y_]=(x^2);Plot3D[f[x,y],{x,-3,3},{y,-3,3},PlotPoints->24,AspectRatio->1,AxesLabel->{x,y,z},ViewPoint->{20,8,1}]

F[x_,y_,z_]=(x^2)-y;ContourPlot3D[F[x,y,z]==0,{x,-3,3},{y,-3,3},{z,-3,3},Axes->True,AxesLabel->{x,y,z},ViewPoint->{20,8,2}]

F[x_,y_,z_]=1-(x^2)-(y^2)-(z^2);ContourPlot3D[F[x,y,z]==0,{x,-2,2},{y,-2,2},{z,-2,2},Axes->True,AxesLabel->{x,y,z},ViewPoint->{20,8,2}]

Clear[f,x,y];
f[x_,y_]=(Sqrt[1-(x^2)-(y^2)]);
Plot3D[f[x,y],{x,-1,1},{y,-1,1},PlotPoints->34,AspectRatio->Automatic,AxesLabel->{x,y,z},ViewPoint->{20,8,1}]

F[x_,y_,z_]=1-(x^2)-(y^2);ContourPlot3D[F[x,y,z]==0,{x,-2,2},{y,-2,2},{z,-2,2},Axes->True,AxesLabel->{x,y,z},ViewPoint->{20,8,2}]

Clear[F,x,y,z];
F[x_,y_,z_]=1+(x^2)+(y^2)-(z^2);ContourPlot3D[F[x,y,z]==0,{x,-3,3},{y,-3,3},{z,-3,3},Axes->True,AxesLabel->{x,y,z},ViewPoint->{20,8,2}]