"Werf" was created to replace the more cumbersome "he or she" and, as such, can be used anywhere the third person singular pronoun would be used. Eg. "Who is this reader and why is werf so upset?"
Most unusually, the pronoun does not decline in its object form, so "werf" can also be used to replace "him or her." Eg. "I don't think anyone here knows werf in RL."
The possessive form of "werf" is "werf's" (or possibly "werfs"). It replaces "his or her." Eg. "What is werf's problem?"
The werfish form of "his or hers" (possessive noun as opposed to possessive adjective) is unclear. The correct form may be "werfs," but the usage has not yet settled down. "Werfself" may also be used as a substitution for "himself" or "herself." Eg. "If every reader would search the archives for werfself, werf would save the writers a lot of time."
As a fairly new addition to the English language, the usage of "werf" is still in flux, although I think the above outlined rules are becoming fairly concrete. Additional, non-standard uses of werf include using it as a general term for people ("Greetings, werfs!") and also as a mild expletive or interjection ("What the . . . werf?").
"Who is this reader and why is werf so upset?"