You will need administrative access to add a field to the system.
1. Admin | Site Settings
2. Select the table you want to add the field to
3. New Field (may need to open the window if on an old build)
4. Enter the name of the field and select VarChar then enter the number of characters it should store and if you want a default value.
Now add the field to the layout, if you are not technical we can assist.
2. TroubleShooting | Templates
3. Select the layout such as contact.html scroll to the bottom left and edit the template entering the new field where you want it and save.
You can also have multiple layouts which can alter depending on the record type being viewed or the stage of work the record is at or the department / language of the person viewing.
We are happy to provide support (training) if needed.