Elementals are beings of pure element, unlike beings of the physical world which are all created by an interplay of all elemental energies. As pure elemental energy, they do not exist on the physical world per se, but they are sometimes "seen" in their natural element, such as salamanders in fire, undines in water, etc.
Elementals are intelligent, although for a large part their knowledge is centered on the concerns of the elemental energy they are composed of. They are not evil but can be mischevious when not properly directed. Elementals are not created, although you can summon and direct them to specific tasks that they are suited for. Great care should be taken when doing so, as they will follow instructions to the letter, and will put their own understanding on instructions that are vague. Like anything else, when used responsibily they are a great asset.
As they are not physical entities, some means of non-sensory communication is required. The most common versions are scrying with a magic mirror or communication with the Astral body or the Body of Light.
Now, it is possible to create an artificial elemental. These are comprised of a single elemental energy and are escentially programed for a specific task. Then they return to the energy they were originated from. They have a limited intelligence and personality.
Hope this helps.