Essentially, any path that you drawn in Flash, that you want to use to make a sub-selection of your artwork, has to be pasted onto your artwork layer and the "outside" portion deleted.
Let's say you imported JPG into Flash of a house, and you wanted to remove the background. First, break it apart so that it's a fill. Then, it can help to draw your manually-drawn pen selection on a new layer above. Once you have traced the house/drawn your selection (making sure it's a closed selection) , copy the lines and paste that onto your layer of artwork. Click outside of the selection and delete the edges.
One could also decide to fill the drawn selection lines, and use that as a mask for the artwork.
Flash has fewer of the drawing tools than Photoshop or Illustrator. But even if this doesn't answer your question, there is a way to do what you want.
That helped a lot. Thank you.