What is pen tool?
The Pen tool lets you create straight lines and smooth flowing curves with greater precision than is possible with the Freeform Pen tool. For most users, the Pen tool provides the best control and greatest accuracy for drawing a clipping path.
To draw with the Pen tool:

• Select the Pen tool .
• Set the following tool-specific options:
• To add an anchor point when you click a line segment and delete an anchor point when you click it, select Auto Add/Delete in the options bar.
• To preview path segments as you draw, click the inverted arrow  next to the shape buttons in the options bar, and select Rubber Band.
• Position the pen pointer where you want to begin to draw, and click to define the first anchor point.
• Click or drag to set anchor points for additional segments.
• Complete the path:
• To end an open path, Ctrl-click (Windows) or Command-click (Mac OS) away from the path.
• To close a path, position the pen pointer over the first anchor point. A small loop appears next to the pen tip when it is positioned correctly. Click to close the path.

You create curves by dragging the Pen tool in the direction you want the curve to go. Keep these guidelines in mind when drawing curves: Always drag the first direction point in the direction of the bump of the curve, and drag the second direction point in the opposite direction to create a single curve. Dragging both direction points in the same direction creates an "S" curve.
Drag in the opposite direction to create a smooth curve. Drag in the same direction to create an "S" curve. When drawing a series of smooth curves, draw one curve at a time, placing anchor points at the beginning and end of each curve, not at the tip of the curve. To decrease the file size and reduce the potential for printing errors, use as few anchor points as possible, and place them as far apart as possible.