Click the Graphics|New|Parametric Graph command to create this kind of graphs. This will cause the Parametric Graph dialog box show. There you can modify it's properties (formula, color, width and style, intervals and so on).

Parametric Graph Dialog box

The X(t) = and Y(t) = boxes prompt you to enter a function's formula. The right hand side of the formulas must be any mathematical expression including constants and an independent variable (parameter) t.

The Parameter tab lets you set ranges and the step for the parameter. Be attentive while manipulating these values. Setting too small step or too wide range causes growth of number of calculations. This may consume much time while building a parametric graph.

The Visible option allows you to temporarily hide a graph without deleting it from the project.

The Intervals tab lets you to choose the space for each line. This makes it possible to draw lines that only occupie part of the (x, y)-axes (not the whole as by default).

Use the Color and Size boxes on the right to adjust the color and the thickness of the curve.