Use the Line Tools to draw various types of straight and curved lines. Clicking the small arrow next to the tool's icon will display a menu containing the sub-tools below:
The thickness of lines is controlled by the Line Width slider on the Option Panel (pictured below).
The Option Panel as it appears when one of the Line Tool are active.
The Start Cap and End Cap controls determine how each end (or cap) of the line will be drawn. The Start Cap is the beginning of the line where you first click the mouse cursor. Available cap choices are Flat, Round and Arrow. The size of the arrow depends on the width of the line. The round option is only noticeable with thicker lines.
The Line Style control determines how the body of the line will be drawn. Available line style choices are Solid, Dash, Dot, Dash-Dot and Dash-Dot-Dot.
If you cannot see the selected line style (especially with 1 pixel line widths) try turning off the Anti-alias option.
Enabling the Anti-alias option will smooth out the normally jagged edges of diagonal lines.
Holding down the Shift key while drawing lines will cause the line to snap to angles in 45° increments. This is helpful when you want to draw perfectly horizontal or vertical lines.