How can I draw a mask in after effects?

[Melanie5E1C]

I am trying to draw a mask layer in After Effects.

I expect that I am supposed to create a new shape layer. Click on the layer. Click on the pen tool. I expect the pen tool to be appearing as a pen nib + a sqaure with a dot in its centre. Instead, it consistently shows as a pen nib with a star. I expect this UX to be when I have not selected the shape layer before I choose the pen tool. It is not the case. I cannot find an option to convert my shape into a path (when I right click, the roto bezier option is greyed out).

I expect that the instructions in this video should be correct: https://www.google.com/search?q=how+to+draw+a+mask+path+in+after+effects&oq=how+to+draw+a+mask+path+...

I cannot force the pen tool to switch to become a path drawing tool. Where is the fucntion that forces this?

[Jose Panadero]

The tool works this way:

- If you use the pen tool over any kind of layer (except shape layers) you will create a mask as soon as you start drawing a shape.

- If you have previously created a shape layer, the pen tool will create new shape paths on this shape layer. In the toolbar, there is a little mask icon to "force" the tool to create masks in shape layers (check attached image)