Use Line 
to draw straight lines in the picture. Set the width of the line with Size
in the Brush section. See Size.
To use Line
-
In the Paint Tab
of the Design Panel 
, click Line 
. -
Choose Paint > Line.
Draw Straight Lines with the Line Tool
-
Select the desired colors for foreground and background in the Color panel. Use Pick Color
if you want to select colors from the picture.
-
Click the Line icon
.
-
Change the line width if desired by selecting a line width in Size
in the Brush section.
-
Drag across the work area from the desired start point to the desired end point to draw a line. A line appears "attached" to the pointer showing the size of the line that will be drawn. The length of the line in pixels is shown in the status bar.
-
Lift the pen or release the mouse button and the line is drawn in the foreground color.
-
Each time you drag and release a new line is drawn, until another feature is selected.