1
general::
Energetically begin an activity, set to work, as in As soon as they had the right tools, they fell to work on the house. This expression is Also often used to mean "begin to eat." Charles Dickens so used it in American Notes (1842): "We fall-to upon these dainties." [Late 1500s]
American Heritage Idioms
2
general::
Phrase(s): fall to someone
Fig. to become the responsibility of someone. • It always falls to me to apologize first. • Why does it fall to me to answer the telephone every time it rings?, Phrase(s): fall to
to begin doing something; to prepare to do something and go to work on it. • She asked for help, and everyone fell to. • Fall to, you guys!
McGrawhill's American Idioms And Phrasal Verbs