Pen

The Pen tool (Create > Polygons > Pen) gives a quick way to create polygons on the fly, and creates the points as part of the process.

To create a polygon with the Pen tool:

Choose Create > Polygons > Pen and click in a viewport with your LMB. A polygon is created using points you define by clicking. If you drag with the mouse button, you can refine the point’s position before you create it, which happens when you release the mouse button. You do not need to click in the same viewport for each point. Once you have the polygon defined as you wish, you can finalize it by clicking the Pen tool off.

If you wish to create multiple polygons, then once you have completed a polygon, move the mouse cursor to where you wish to place the first point of a new polygon, click the RMB, then continue to build the new polygon using the LMB.

While the pen tool is active, you can click on and drag any point using the LMB to edit its position.
If you create a new point in your polygon by clicking to closely to an existing point, Modeler can think you are editing the existing point and not create the point. If this is the case, simply click at a location that is not close to an existing point, then drag the new point to its desired location.

The Add Point button allows you to interactively add a point to your newly created polygon.

The point will be positioned at the same location as the last created point, so may not be obvious until you change its position either with the numeric panel, or by clicking on it and dragging with the LMB .
Once you create a polygon, you’ll want to view it in the Polygon Selection mode to see if its surface is facing the correct direction based on the normal, as discussed elsewhere. If you are using the Back view for example, creating points clockwise will make a polygon with its face or normal facing you. Counter-clockwise creation of the points will make a polygon that faces away.