The Orlah app use is to determine when it is biblically permissible to eat the first of its fruit based on the age of the tree from the day a seed is planted. It is based on a period of approximately 3 years based on the Hebrew calendar as well as which particular period (3 scenarios) the seed is placed in the ground. It also takes into account if one lives in Israel or in the Diaspora. The calculations are done in the Hebrew calendar after entering the Hebrew or Gregorian date and results given in both calendars.
During particular planting dates two options are given based on rabbinical studies from two prominent sources between the 11th and 13th century and codified by the 15th century Code of Jewish law. These options are either lenient or stringent.