The help for “Preview” says: "You can choose a standard text sample from the drop-down list or enter your own text.
I have FontCreator 6.0 Home Edition (Licensed). Is the “enter your own text” feature only for the professional version or can you please explain HOW? as it won’t let me into the textarea and I can find no option for it. 
It is available in bot Home and Professional Edition. To enter your own text in the Preview toolbar, just click inside the text area of the drop-down list.
Note: The Preview toolbar is useful in many ways, but for a better preview we suggest you use the Test Font window (F5).
Click in the drop list at the top of the Preview Toolbar, not in the preview area itself.
The Preview Toolbar shows text with kerning, whereas the Font Test Window does not. To enter several characters into the Preview Toolbar, select them in the Overview with Control Click or Shift Click, then press the shortcut “P” to add them to the Preview Toolbar.