Ok, so people don't seem to understand what portal blocks are. Now there are various types of the blocks, and essentially they all do the same thing: go in one, come out the other.
It does this by either: a) you place an entry block down, then place an exit block somewhere else. The entry block is visible and the exit is not. When the player clicks the entry block, they will be teleported to the location of the exit block.
b) A different kind of portal block is that that is either water or air. It is the exact same as above but the player simply walks through the block(s) instead of clicking it.
Now, another issue that players have been misunderstanding is that when I say allow them, I do not mean in game.
I simply mean allow them to be incorperated in maps when they are being built for the server. This would only work though if the teleportation rules or wizard kicks could be coded around which I know they can: eg: [player] is trapped inside a block! followed by a teleportation to the spawn.