If you can find your glyph in one of the symbol character sets, then you can map it there. If it is a unique symbol the character set to use is the Private use Area.
Use Insert Character (if you have the trial version or Professional version), as this does the mapping and inserts a glyph in one stage. With the Home version, you must insert a glyph, then add mappings as explained above.
This illustration shows how to insert a whole range of ready mapped characters from the Miscellaneous Symbols. Just select a character from the Private Use Area character set instead if that’s what you want.
To type these characters in your word-processor you will need to use the insert symbol dialogue, assign a shortcut, or remember its decimal code-point and hold down the Alter key while typing the decimal code-point on the Numbr pad (this method works in WordPad). For example, to type the Fleur-de-lis symbol illustrated, you would hold down Alter and type 9884.
To change the display in dialogues from Hex to Decimal, go to Tools, Options, General, and select Values, Decimal.
See also: this tutorial on the Insert Characters Feature