when did our current calender come into use?
1582
It depends on what you mean by the question. The so-called Gregorian calendar was adopted by Great Britain in 1752 and went into use in the British colonies at the same time. In some countries the reform had been adopted as early as 1582, whereas in Russia the old Julian calendar was in use until 1918.
The Gregorian calendar is named for Pope Gregory XIII, who ordered 10 days dropped in 1582 (so the day after October 4 was October 15), to bring the vernal equinox back to where it had been at the time of the First Council of Nicaea in 325 (when the rules for calculating the date of Easter were adopted). The Julian calendar had a slight error that caused it to be off by one day in 128 years, and the errors slowly built up.
The Julian calendar is named for Julius Caesar, who reformed the Roman calendar in 46 B.C., making it a year with 365 days and one more every fourth year. Before that the Roman calendar was irregular and a whole month was inserted in some years to keep the months in line with the seasons, but sometimes the month had not been inserted when needed, so Caesar had to add an extra 90 days to the year 46 B.C. to get things back on track.
The original Roman calendar goes back to early Rome but I don't think they can put an exact date on when it was introduced.