Refer to figure.
The flight directors provide information for the pilot to join a desired path with the optimum attitude. Flight director information supplied by an FD computer is presented in the form of command bars on the Attitude Director Indicator (ADI).

• The vertical command bar of the FD supplies information about the direction and magnitude of the corrections to be applied to the bank angle of the aircraft. The vertical bar is always associated with the roll channel.
• The horizontal command bar of the FD supplies information about the direction and magnitude of the corrections to be applied to the pitch angle of the aircraft. The horizontal bar is always associated with the pitch channel.

When tracking the glideslope, the command bars will indicate at which angle you should pitch and bank the aircraft in order to get back on the glideslope. In other words, it will indicate the correction to be applied to the pitch and bank angle in order to capture and then readapt this pitch and bank angle so that you follow the glideslope.