Go to the frame where you want to set a keyframe.
On a attribute in the Attribute Editor
Set Key

Go to another frame, change the attribute value, and Set Key

If keyframes are set to attribute, the checker icon turns to connection.
and attribute tabs appear.

Keyframe time and keyframe value are displayed in spread sheet.
You can edit them.

If you want to edit values in the Graph Editor,(or want to delete keyframe or add keyframe)
click Select button in the Attribute Editor,
and open the Graph Editor.

If you change the material transparent, you should change the Transparency value,
and also change Specular Color, Reflectivity.
because Specular Color value and Reflectivity value are added to brightness of the surface.