Keys are arbitrary markers that specify the property values of an object at a particular time. Setting keys is the process of creating the markers that specify timing and action in your animation. Animation is the process of creating and editing the properties of objects that change over time.
Once you create an object you want to animate, you set keys that represent when the attributes of that object change during your animation. Setting a key involves moving to the time where you want to establish a value for an attribute, setting that value, then placing a key there. In effect, you are recording a snapshot of the attribute at that time.
You can rearrange, remove, and duplicate keys and sequences of keys. For example, you can copy the animated properties of one object onto another, or you can stretch a chunk of animation over a longer period of time than you originally keyed.
The Attribute Editor displays attributes you can edit and key (animate). You can key attributes by 
-clicking them in the Attribute Editor, and then selecting Set Key from the pop-up menu. This menu is not available for attributes you cannot key. See Add keys.
Certain attributes are assigned a keyable status by default in Maya. For example, all objects are assigned the following keyable attributes:
Keys in the Channel Box, Graph Editor, and Dope Sheet
You can use the Channel Box for keying operations on attributes of selected objects.
You can also use the Graph Editor to edit and key animation curves for previously animated objects, and you can use the Dope Sheet to set timing and keys for objects.
