I'm not quite sure what exactly you're confused about, but this is
exactly the situation our school (K-8) is having. Our PTA
board CLAIMS that according to state mandates they
CAN NOT raise funds for a lot of things that would greatly benefit our school (both physical equipment and programs). After some investigation, it turns out that their claims aren't supported in the PTA by-laws or procedures literature--it doesn't say "shall not" but instead "should not" when it comes to supplying things the national/state PTA feels the Board of Education should be handling. Make sure your PTA actually CAN NOT do certain things before you believe everything the board tells you! PTAs all over the US and in our own state (and even town!) are doing many of the things our PTA board told us they COULDN'T do. In the end, no one in any of the other projects involved in our school felt it was beneficial, or worth the fight, to make the board do something they obviously did not want to be involved in. But I digress.
As a result, there is the organization I head raising money for a playground now (and hopefully for other materials/programs later), and a couple of other committees for things like dances and grade trips. It's not at all confusing, but it doesn't in any way support a cohesive nature that builds a sense of community. It also creates a sense of resentment among many of the parents in the school community, because they now see "the PTA" as a "them" (which most of us pay dues to belong to!) that is a self-righteous entity because it denies the children so many things that could enhance their educational experience by insisting it's the BOE's responsibility. They way most people look at it is "yeah, well woulda-coulda-shoulda but in the end my kid doesn't have a playground, musical instruments, a well equipped art program etcetera etcetera.(I know MichelleB's feelings about this, and that's she's understandably wincing at those who wreck the good name of the PTA

!
How do we handle it? The group I'm currently the president of is hopeful that the PTA's new board (taking effect with the next election) will be more willing to take on responsibilties it's been shirking. While our group understands that because of its nature the PTA isn't a fundraising entity, we hope to work closely with them from now on to raise monies that fill in those gaps. If people are as confused as you say, if I were you, I'd talk frankly with ALL the groups involved to get information.
The best thing to do is GET INVOLVED and BE INFORMED. Make your own decisions based on ALL the pieces of information you get. Just remember that all anybody really wants is to help our children enjoy and do well in school, and let that be your guide!