The Selection mode (Image selection) is used for selecting in a View (selecting a part of a sequence, selecting nodes in a tree etc.). It is also used for moving e.g. branches in a tree or sequences in an alignment.

When you make a selection on a sequence or in an alignment, the location is shown in the bottom right corner of the screen. E.g. '23^24' means that the selection is between two residues. '23' means that the residue at position 23 is selected, and finally '23..25' means that 23, 24 and 25 are selected. By holding ctrl / Image command_key_web you can make multiple selections.