Why there is 28 days in feb only why others months not have days?

February does not always have 28 days. Every four years, which are called leap years, February receives an extra day which makes that year, leap year, having 29 days of February which makes the year 366 days in one year instead of 365.

All months do have days. January - 31 days, March - 31 days, April - 30 days, and so on. All the reasons behind all of this has their origins based on different historical cultures who were the first to keep up the time using different forms of calenders.