Packets can be selected in the Capture tab via any combination of clicking, Command-clicking and shift-clicking. The up and down arrow keys also change the selection.
Double-clicking on a packet in the Capture tab is a shortcut for switching to the Decode tab.
FrameSeer uses the most-recently-selected packet for certain operations, such as decoding, searching and selecting by criteria. The selection also controls what is copied to the clipboard and what is exported. See copying captures to the clipboard and the Save Selection... command for more information.