Koey,
Painter's Shape Tools and Text Layers
In Corel Painter, the Pen tool, and other Shape tools (Quick Curve, Rectangular Shape, Oval Shape) are vector-based and are used to create vector-based bezier curves and lines. Vectors are lines or curves defined by anchor points at either end of the line or curve. Any object created using the Shape tools is a Painter Shape and appears on its own above the Painter Canvas.
Vector-based Shapes can be scaled up or down without loss of image quality. Painter's Text Layers are also vector based and can be converted to Shapes, then edited like any other Shape using the Shape editing tools (Shape Selection, Scissors, Add Point, Remove Point, and Convert Point).
Below is an image showing a vector-based curve being edited by pulling an anchor point's wing handle to follow a curve painted with the Pencils' 2B Pencil variant:

Here's an image from one of my threads in the Sandbox forum Images Created from Text. It was created by typing Text, converting it to Shapes, then using the Shape editing tools to alter it and turn it into an image that spells itself:
As Scott mentioned in an earlier post, the Pen tool can be used to make selections. Here's a very nice tutorial by John Derry that explains and illustrates the process in detail:
The Shapes Path Tool as Precise Selection Tool in Corel® Painter™, by John Derry
To learn more about Painter's Shapes, read the following:
Painter X Help > Help Topics > Contents tab > Using Shapes
Painter's Brushes
Painter's brush variants, on the other hand, are used to paint pixel-based brush strokes. When the image is Resized upward, it can often lose image quality since the program has to add extra pixels and "guess" what colors those extra pixels should be based on existing/surrounding pixels.
As Tom suggested, many artists use the Pens' brush variants to create line art.
Here's a tutorial about inking line art that may help you, from the October 2006 issue of The Painter Canvas newsletter:
Inking for Comics, Cartooning, and Manga in Corel Painter, by Jared Hodges
Jinny