Using the Tube function to create a torus from an equation for the curve

Graphics3D[
 Tube[
  BSplineCurve[
   {{-3/2, 0, 1/2}, {-3/2, -3/2, 1/2}, {0, -3/2, 1/2},
    {3/2, -3/2, 1/2}, {3/2, 0, 1/2}, {3/2, 3/2, 1/2},
    {0, 3/2, 1/2}, {-3/2, 3/2, 1/2}, {-3/2, 0, 1/2}},
   SplineDegree -> 2, 
   SplineWeights -> {1, 1/Sqrt[2], 1, 1/Sqrt[2], 1, 1/Sqrt[2], 1,  1/Sqrt[2], 1}, 
   SplineKnots -> {0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 4}], 
  1/2]
 ]

Adapted from an example in the docs for Tube:

PieChart3D[{1}, ChartElementFunction -> "TorusSector3D", 
 SectorOrigin -> {Automatic, 1}, BoxRatios -> Automatic]

Here is the torus using Graphics3D and Tube:

Graphics3D[Tube[Table[3 {Cos[p], Sin[p], 0}, {p, 0, 2 Pi, Pi/30}], 1],
  Axes -> True]

You can also use Tube as a styling directive with ParametricPlot3D:

ParametricPlot3D[3 {Cos[p], Sin[p], 0}, {p, 0, 2 Pi}, 
 PlotStyle -> Tube[1], PlotRangePadding -> Scaled[.15]]