To align two or more objects, first select these objects:
To select multiple objects on the Stage, hold the Ctrl or Cmd key and click the other objects. Click once more on an object to deselect it. (Once multiple objects are selected, you can move, resize, cut or copy them all in one operation.)
To select multiple objects directly on the Timeline you can either hold the Shift key to select a group of consecutive objects or the Ctrl or Cmd key to select multiple, non-consecutive objects on the Timeline. This way you can move a group of objects to another point on the Timeline.
Then click the Align Icon in the bar above the Stage and choose your align option.
Please note that, when aligning objects, only the bounding boxes are aligned. For some objects, the bounding boxes do not always visually match the object edges, because they include additional space for object options or animation effects. In that case, it is better to manually align the objects.