Plot — curves of one or more functions

Plot3D — 3D surfaces of one or more functions

ContourPlot — contour plot for a function

or curve

ContourPlot3D — 3D contour plot for a function

or surface

DensityPlot — density plot for a function

ParametricPlot — 2D parametric curves or regions
ParametricPlot3D — 3D parametric curves or surfaces
RegionPlot — 2D regions defined by inequalities
RegionPlot3D — 3D regions defined by inequalities