Automatically make a vector from an existing selection by using the Make from Selection function in the Vector Menu.
- Create your selection using one the the selections tools; Lasso, Rectangular Selection Tool or the Magic Wand.
- Add a vector layer to your design, or activate an existing vector layer.
- Go to Vector Menu > Make from Selection.
If the resulting vector is not smooth enough, you can use the Smooth feature to improve the results.
You can also use the Select Vector Tool to adjust the shape until you achieve the results you need. You can also view the vector as a filled shape by going to Vector Menu > View as filled.
If you want to remove some nodes, select the Select Vector Tool from the Tools Palette and ⌘ (command key) click on the nodes you want to remove. This can have the effect of smoothing out the vector shape.