Let’s consider that we are in January 2018 here.
The incorporation date is the month and year when you officially founded your company. For example, Budgeto was founded on April 18, 2012. Our incorporation date in BUDGETO is APRIL 2012. In BUGDETO we can enter historical data starting April 2012 till December 2017 (the last completed calendar month considering we are in January 2018).
The start of operations date as the same purpose as the incorporation date, but it is for business that isn't in business yet. For example, if you plan to launch your business in March 2018, your start of operations date will be in March 2018.
Your budget will start in March 2018 and you will not be able to enter anything in the HISTORICAL DATA (we cannot enter future data in the past!). As time pass, you will eventually have access to the HISTORICAL DATA once you reach April 2018.