The next three items on the menu,
Convert to Line,
Line Before, and
Line After, pretty much do what they say and are only available when the selected node has curves.
Convert to Line will convert both sides of the node to lines, making it a tangent node.
Line Before or
Line After simply changes the curve on one side or the other to a line. "Before" refers to the portion of the contour behind the node where the round curve handle is and "after" refers to the portion of the contour ahead of the node where the pointy handle is.
That pretty well covers the node type options in Paint Shop Pro. Armed with this knowledge, you can become master of your nodes. Take some time getting familiar with node types. Lay down some shapes and see what you can do by adding curves or lines and changing to different node types. Once you've mastered node editing, you'll be able to fine tune your drawings and shapes with great precision.