What does "tweak left" mean? In Object Mode, the "Select" menu drops down to "Box Select."  The keyboard shortcut shown for this is "Tweak Left."

What does "Tweak Left" mean?  How am I supposed to use this keyboard shortcut (or mouse shortcut)?
You probably have a test build with a tweak patch. Yes, tweaking involves mouse. 


  (...) drag and let go via either left or right click, which most applications have.


This means you click on an object, drag it while holding down the mouse key and release the key when you're done.

You may also read the posts by a pansi and Fligh users