Help me understand the explanations of the Tengwar...

[Peter_20]

Alright, in the LOTR Appendix, Tengwar is explained; however, Christopher kinda seems to point on two different interpretations of some characeters.
Sometimes he goes "g (or gw)" and so on.
Of course this means the character in question is used in two different ways, but what does this mean?
Are the alternatives written within parenthesis the Sindarin version, or what?

[Earniel]

I've always been more at home with the dwarf runes, but this thread may be of use: Writing in Tengwar (http://entmoot.tolkientrail.com/showthread.php?t=5568) It can sometimes be very helpful to look through old threads. ;)