This button lets you copy a range of keyframes from one time to another.
Clicking this button creates a keyframe at the current time in the envelope window, using the current value. Usually you will create new keyframes by simply clicking in the envelope window, however, this button lets you manually create a keyframe when you already have the current time slider at the proper position, and your current control is set to the value you want for the keyframe you are creating.
This button will delete the current keyframe from the envelope. You cannot delete the keyframes at 0% and 100% in time.
This button will move the current time slider to the previous keyframe in the envelope.
This button will move the current time slider to the next keyframe in the envelope.