ok now im confusedFollow

when i first bought WoW i was under the impression that on a pvp server any character could just go whack eachother and kill them even if they were both horde or both alliance, and i hated this idea so i went to a pve server, just today i created a character on a pvp server and when i tried to attack another tauren it said invalid target, was i doing something wrong, or had i just wasted all the time i spent with my pve server character?

The PvP server is pretty much a FvF or Faction vs Faction server. It goes like this:

1) You cannot attack a member in the opposite faction if you are on their territory in vice versa.

2) In contested territory, PvP happens freely between both factions.

3) Like in PvE servers, NPCs are always fair game.

Why would you want to be able to attack other Horde members? Those are your allies.