The position of the playhead is important when you add objects to the scene and when you create animations. When you add an object to your sequence, it's added to the timeline at the position of the playhead. Similarly, when you create a keyframe, it's inserted at the current position of the playhead.
To move the playhead, select a point on the time scale. You can also select the playhead and drag it to a new position.
For more accurate placement relative to existing objects, you can use the jump to icons: and .