Answer:
A portal is a quick, very quick, way to get from where you are to one of the capital cities or Shat/Dalaran. Only mages can make portals and they require a Rune of Portals to use. Druids can use the moonglade teleport to travel to moonglade, but they cannot bring anyone with them. Death Knights can use a Death Gate to travel to Ebon Hold, the death knight only area, but again, they cannot bring anyone with them. Some NPC factions have a ring or tabard that will teleport you to dalaran or the tournament grounds, but those cost money and rep.