We notice that for every 4 years a day is added to February. It is strange to add a day in between right?

However, the earth's orbit takes 365 days and 6 hours to complete one year and an extra day every four years is added to keep calendar seasons synchronized with solar seasons.

February was chosen as the month to have the leap day as it is the only month without 30 or 31 days.

References:

https://minnesota.cbslocal.com/2016/02/29/why-is-leap-day-in-february/

https://www.scienceabc.com/eyeopeners/why-do-we-have-a-leap-day-leap-year-after-every-4-years.html