Choose the Pen, the Style and the Tension, from the row of buttons 2, 3 and 4. Now clic on one of the three firsts buttons in the first row, depending of the kind of curve you want to draw. In TVPaint Animation, click into your project to define the control points. They will be temporary connected with lines, this will give you a visual feedback while drawing. The final curve will go through all the control points. Use a double-clic to define the last point. Then the curve is drawn.
Fig. 2 : 3 curves samples produced from the control points you can see up left.
Fig. 3 : Closed and filled curves.
You can change the Pen, the Style and the Tension for the last curve. Select the new options and click the ReTrace button. Of course, you will have to delete the curve in TVPaint Animation first.