Menu "View" - "Align selected" is available when more then one person are selected and contains two subitems:

Align horizontally - selected frames are aligned horizontally, as shown on the example:

Before alignment:

After alignment:

After selecting the frames to be aligned, it is necessary to tell the program which frame you wish to align the others to. Do this by clicking on that frame. If you do not do this, the program will remind you.

Align vertically - the centers of the selected frames are set on a vertical line:

Before alignment:	After alignment:

Just as in the previous case, after selecting the frames to be aligned it is necessary to tell the program which frame they are to be aligned to.

See also:
Menu "Edit" - "Undo move"