  This paper aims to provide an introduction to a basic form of the ${\bf
Q}$-tensor approach to modelling liquid crystals, which has seen increased
interest in recent years. The increase in interest in this type of modelling
approach has been driven by investigations into the fundamental nature of
defects and new applications of liquid crystals such as bistable displays and
colloidal systems for which a description of defects and disorder is essential.
The work in this paper is not new research, rather it is an introductory guide
for anyone wishing to model a system using such a theory. A more complete
mathematical description of this theory, including a description of flow
effects, can be found in numerous sources but the books by Virga and Sonnet and
Virga are recommended. More information can be obtained from the plethora of
papers using such approaches, although a general introduction for the novice is
lacking. The first few sections of this paper will detail the development of
the ${\bf Q}$-tensor approach for nematic liquid crystalline systems and
construct the free energy and governing equations for the mesoscopic dependent
variables. A number of device surface treatments are considered and theoretical
boundary conditions are specified for each instance. Finally, an example of a
real device is demonstrated.
