Hi Nicole,
One problem the English language has had to face is finding a gender-neutral singular pronoun. "It" doesn't work because that is already used for non-human things. The old usage of "he" is no good because it clearly excludes women.
One current solution (aside from some very silly words made up by PC advocates) is to take the plural 3rd-person "they" and apply it to "he/she". This may not be as bad as it seems, because we had already replaced the 2nd-person singular "thou" with the plural "you" some centuries back.
"Themselves" makes sense because it's consistent with the plural. I think some users have taken to writing "themself" to make it clear that it's a 3rd-person singular, not the plural.
We're still working it out, but a safe bet is to avoid using "themself" because it sounds contradictory ("them" is still a plural!)... expect to be corrected for bad English sooner or later, if you do use it.
One could argue for hours over this. ^^