Following is a tutorial that will hopefully help explain node editing to you.
This is for PSP 8.
Although many aspects are the same in both versions, some are different.
If you are working in PSP 9 please see here for node editing.

Nodes are tiny boxes placed along the outline of your Vector shape. When you draw a Vector shape with the Preset Shapes tool, you will see about 9 nodes. You use these nodes to adjust the whole shape as one.
Select the Object Selection tool on the tool bar to adjust the nodes. You can not add or delete nodes on the shape this way.

For example if you click on the top left node and drag it up and to the left, it will increase the size of your shape as a whole. If you click on the node on the left center and drag it toward the center of the shape, it will make the shape narrower as a whole. Drag it out and it will make it wider.
You can also use the right center node the same way.

Hold the Shift Key and drag any node and it will drag it in a diamond direction.
Hold the Ctrl key and drag any node and it will drag it in a triangle direction.
The node to the right of the little circle in the center of the shape is to swivel the shape. Click on it, hold it and you can swivel it around.
Just remember that these nodes will change the shape as a whole.

Now to go into more advanced node editing.
Click on the Pen Tool on the tool bar.
This tool will allow you to add, delete and adjust nodes on your shape. Each node will have a handle on it. You won't see the handles until you click on the node to select it.The handle has an arrow at one end and a circle at the other. These handles give you more control over how to adjust your shape.

The nodes can be set in several different ways but to start, you only need to know a few of them. Once you get the hang of using Vectors, you can check out the other settings for the nodes and learn what they do.
For now though, I am only going to show you three node types.
To set the node type..right click on the node you want to set and go to Node Type, then choose the one you want.

Asymmetric
Asymmetric basically means that each side of the handle is attached to the node and they move together but in opposite directions when you swivel them. However, you can pull one handle out farther than the other. It doesn't matter which handle, you can pull either one of them . The same goes for swiveling...you can swivel it by pulling either handle up or down.
Play with them by pulling and dragging them around and it won't take but a few minutes to see what all you can do with this setting. I rarely use this setting.

Symmetrical.
This node type is almost the same as the Asymmetrical except that you can't pull either of the handles out farther than the other. If you pull on one handle, the other side pulls out the same distance.
This setting is what I use all the time to get smooth rounded curves.

Cusp
This is what you use to get a corner in your shape. Basically it means that each handle moves independently from the other. It's kind of like they are attached to the node but separate. You can swivel or pull each handle separate.

You can change the node type at any time by right clicking on it and going to Node Type, then selecting the type you want.

To add a node anywhere on the shape, hold the CTRL key down and click where you want the node to be.

To delete a node, hold the CTRL key and click on the node you want deleted.

When you are drawing, you add or delete nodes and adjust them to form your shape.

A good way to get used to node editing is to open a new canvas, draw a shape, then play with the nodes. It really only takes a few minutes to get used to them. I only use two node types... Symmetrical and Cusp. With just these two I can do anything I want in forming a shape. A good way to remember which one does what is to associate their first letters with what they do.
Symmetrical = S = Smooth
Cusp = C = Corner.