In Advanced mode each element has a separate layer in the animation timeline. This lets you change where each element is in the stack of elements, hide elements, or lock elements so you can work more efficiently.
When you're in Advanced mode you can individually animate any elements you wish to while optionally modifying transition times and easing for each animation. You can also add event markers and event labels to the timeline, which lets you use events to control animations, and use the timeline to trigger events.
The yellow vertical line in the timeline is the playhead. It shows where you are in the animation. You can drag the playhead forward and backwards to fine tune your animation, or to add new keyframes.
To switch to Quick mode:
Click the Quick mode icon . Each timeline location with a keyframe will be converted into a Quick mode scene, creating a Quick mode version that preserves your animation.