A spell’s components are what you must do or possess to cast it. The Components entry in a spell description tell you what type of components it has. Below are the three types supported by Dungeons and Dragons Online. In Pen & Paper, there is also a Focus component. This is not specifically in DDO, as it is assumed you have your focus with you at all times.
A verbal component is a spoken incantation. To provide a verbal component, you must be able to speak in a strong voice. Spells that require this are not castable if, for some reason, you cannot speak.
A somatic component is a measured and precise movement of the hand. You must have at least one hand free to provide a somatic component.
A material component is one or more physical substances or objects that are annihilated by the spell energies in the casting process. Some spells require the basic spell casters material component, such as Pinch of Fine Sand. These components can be purchased at Archane or Divine spell component vendors.
A list of material component per class and spell level can be found on the Material Components page.