If you click with left button of the mouse on a curve in a selected view, you select the curve. The curve will change color, and its control points will appear on display ( you will see a little square for any control point ). If you click again far form the curve, you deselect it.
If on a selected curve you press the left button of the mouse in a control point, the square will become red., you have selected the control point. There are some actions you can do in this situation:
press key `d'. This delete the control point.
press key `a'. A new point control will be added in the cursor position.
press key `m'. You move the control point position. The new position will be the same of the cursor.
You can also click and drag on a control point to move it.
You can use the grid ( Option|General... ) to limit the positions of the point.
You can use the polyline in many way. You can use it to build brep objects.
Remember to work always in the Top view!
It is possible to build rotation brep or sweep brep.
4.3.3.4