what's the begining date or the date they first add up the taxes and whens the last day they count your taxes

Answer 1

For personal returns, the tax year is the calendar year.

Answer 2

If you are a worker, working for someone else, your income, taxes etc begins January 1st (which can include income, taxes that were earned the last few days of the year before if your paycheck falls after the first of the year. It ends the 31st of Dec. and the same applies, the last few days of the year could possible go over to the next year depending on when your paycheck is written.