Elementals come in two diffrent types, there are those that are thought of as spirits of the four elements and those that can control these elements at will.  The element masters of air would have the ability over air, they can control anything from a simple breeze to gale force winds,  using this power they can also fly upon the air currents going where they wish and benifiting from their abilities.  In most stories air folk are supercillious and flighty as their element.   Water elementals have control over water, they can control the waves and make waves in still water, in some books they can breath under water for indefinate periods of time.   Water elementals are thought of as being a calm and soothing force.   Earth elemtals can control soil rocks and in some cases animals and humans.  Earth elementals can also heal people as they have close connection to the body.  They are quite literally thought of as down to earth.  Fire elementals have ability with fire, this seems to be the most dangerous of elements for obvious reasons, people and fire do not mix well.  In some reports Fire elementals are resistant to the flames they control.  Fire elementals are often given to fury and are as volitile as their element.  The four elements sometimes have a fifth called spirit, which can replace Earth's ability to control people.  In some cases they can see into the minds of others if that an be believed.  All elementals seem to be quite cool to me, I wish I had control over one of these elements.