Use lines to divide faces and construct geometry.
You can draw lines on the X, Y, or Z axis and also on existing geometry. When you snap to an axis, a colored line extends beyond the line you are drawing indicating which the axis you are drawing on. You can see the length of the line as you draw, and you can manually enter a specfic length by pressing tab and enter a value.
Line colors by axis:
To specify a length, simply type a dimension value, and an Edit Dimension dialog will appear. Hit OK or press Enter to accept the value.
X = Red
Y = Green
Z = Blue