I'm currently introducing those tags while working through the list of unanswered questions from behind. Depending on the question, there are different needs for help and I tag those questions which didn't get any attention so far, because they are about help needed but not yet given.
coding-help is about help needed in doing PHP coding in a wordpress related context. Probably such a question could be moved to a PHP related coding forum/wiki, but as it appeared here in wordpress context, to answer that wordpress related question, some help in coding might be needed to answer that question.
support-help is about assisting the question asker about debugging and tackle configuration issues with the wordpress installation in question and/or the server it's running one.
server-help is even more specifically tagging questions asking for help configuring a server to run wordpress.
css-help is quite the same like coding-help, but about how to write css instead of how to write php or javacsript.
Well if those questions wouldn't have the help suffix you didn't know that this is about helping someone, right? This is in contrast to questions where that someone just asks and you know the answer to because it's knowledge that is already available.
Older questions can then be answered based on their *-help tag, e.g. a coder can look into those and pick them up.
spamming-help is not of use right now but it could be used if the one who is asking a question is actually asking for help setting up a wordpress based splog. It might be useful when reviving an old question that might have not got any attention because some community users might not want to support such a wordpress administrator. But well, this is sort of contradictory, as it's not easy to say, subject to opinion etc.