The red vertical bar with a handle (red flag) at the bottom is the scrubber. The scrubber identifies the current temporal position of the view displayed on the canvas, and its timecode displays in the toolbar.
You can scrub (move) through your project by using the mouse to grab the top handle (in the time scale) and moving it right or left. Notice that as you use the scrubber to scrub your project, the canvas updates in real time.
You press the Home key (or select Mark > Go to > Project Start) to jump the scrubber to the beginning of the timeline, and the End key (or select Mark > Go to > Project End) to jump to the end. You can also use the left and right arrow keys to move the scrubber a frame at a time—or select Mark > Go to > Previous Frame or Next Frame.
