Plot3D[Sin[x+y^2],{x,-3,3},{y,-2,2}]

Restrict the domain:

Plot3D[{x^2+y^2,-x^2-y^2},{x,-2,2},{y,-2,2},RegionFunction->Function[{x,y,z},x^2+y^2≤4],BoxRatios->Automatic]

Plot the contours of a function:

ContourPlot[Cos[x]+Cos[y],{x,0,4Pi},{y,0,4Pi}]

Plot an equation (specific contours):

ContourPlot[Cos[x]+Cos[y]==1/2,{x,0,4Pi},{y,0,4Pi}]

Plot a 3D contour surface:

ContourPlot3D[x^3+y^2-z^2==0,{x,-2,2},{y,-2,2},{z,-2,2}]

Plot several contour surfaces:

ContourPlot3D[x^3+y^2-z^2,{x,-2,2},{y,-2,2},{z,-2,2}]

Use styling to emphasize features:

ContourPlot3D[x^4+y^4+z^4-(x^2+y^2+z^2)^2+3(x^2+y^2+z^2)==3,{x, -2,2}, {y, -2, 2}, {z, -2, 2},Mesh->None,ContourStyle->Directive[Orange,Opacity[0.8],Specularity[White,30]]]

x=1/2;
ContourPlot[x^4+y^4+z^4-(x^2+y^2+z^2)^2+3(x^2+y^2+z^2), {y, -2, 2}, {z, -2, 2},Mesh->None,ContourStyle->Directive[Orange,Opacity[0.8],Specularity[White,30]]]
Clear[x]